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Guidelines for understanding and managing risks in recreational waters: Water quality assessment

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Introduction

Water quality assessment at recreational water areas can be included as part of a risk management strategy and may serve many functions. It can be used to:

Water quality monitoring may be conducted routinely or may be carried out for specific hazards (for example, during a suspected outbreak or in response to an unusual wastewater discharge) when there is evidence of water quality issues or when further information is needed. The level and type of monitoring required will vary between recreational areas and should be determined by the appropriate regulatory and management authorities.

Routine monitoring usually includes indicators that inform beach managers about the potential impacts of fecal contamination, such as the fecal indicators E. coli or enterococci (see Monitoring for fecal indicators below) as well as other types of parameters (for instance, cyanobacterial indicators or toxins, aesthetic quality, physical hazards, specific hazards) (see Monitoring for cyanobacteria and their toxins, and Other monitoring).

Targeted water quality monitoring for specific hazards may be necessary in the following situations:

Routine and targeted monitoring data can also be used in setting up predictive models for beach areas (see Predictive water quality methods).

Monitoring for fecal indicators

Recreational waters are routinely monitored to characterize the level of fecal pollution. A monitoring program for a recreational area (when required) should be developed based on the information obtained as part of the recreational area's EHSS. A well-structured and planned monitoring program is essential for assessing and communicating information on the quality of recreational waters.

The primary fecal indicators used for routine monitoring are E. coli or enterococci. Guideline values have been developed for these fecal indicators to protect public health. Other fecal indicators may provide valuable supplemental information with respect to the fecal contamination of recreational waters. They may be included in a monitoring program or for fecal source tracking studies. A notable area of current research is the development of water quality risk-based thresholds for some of the other fecal indicators (for example, coliphages, HF183 and crAssphage microbial source tracking marker genes for human sewage). Further information can be found in Section 3.2 and in the Indicators of Fecal Contamination guideline technical document (Health Canada, 2023).

There are a number of factors that can influence the spatial and temporal microbiological quality of a recreational water body. For example, studies have reported higher concentrations of indicator bacteria in samples collected in the mornings, with concentrations decreasing later in the day (U.S. EPA, 2005a; U.S. EPA, 2010). In addition to the time of day, the type and periodicity of contamination events (both point and non-point sources), recent weather conditions, the number of users frequenting the swimming area and the physical characteristics of the area itself can impact water quality. Consequently, significant day-to-day (and within-day) variation in indicator organism densities has been well documented for recreational waters (Leecaster and Weisberg, 2001; Boehm et al., 2002; Whitman and Nevers, 2004; U.S. EPA, 2005a). As a result of this variation, it is important to have a well-designed monitoring program and to understand how the information obtained can be best used to inform public health decisions. Monitoring using polymerase chain reaction (PCR)-based methods has the advantage of providing more rapid results for decision-making purposes, sometimes within a few hours of the time of analysis. Development of predictive beach water quality models may also be beneficial where water quality is variable and sufficient data are available. All monitoring data collected, whether daily or less frequently, provide information that allow the responsible authorities to more easily observe water quality trends and to make more informed decisions regarding the area's overall suitability for recreation.

Decisions regarding the frequency of monitoring, the areas to be monitored, choice of indicators and methods, and monitoring program design (including the number of samples and the locations where they should be collected) will be made by the appropriate regulatory and management authorities. Further information on monitoring methods, including advantages and limitations, can be found in Health Canada (in publication). Monitoring programs should capture the spatial variability of beach areas and incorporate information derived from the EHSS, taking into account recommendations made about priority areas of concern.

There should be a documented monitoring plan for all monitored beaches, providing, at a minimum, instructions on:

In general, waters regularly used for primary contact recreational activities should be monitored for fecal indicators at a minimum frequency of one sampling event per week during the swimming season. Each sampling event may require the collection of multiple samples. A weekly monitoring strategy allows comparison of the water quality results to the guideline values. It is also useful to alert managers and responsible authorities to more persistent contamination problems that may have developed and allows them to make the necessary decisions within a reasonable time frame. More frequent monitoring should be considered for high-use beaches. These recommendations are consistent with those published by the United States Environmental Protection Agency (U.S. EPA) in its 2012 Recreational Water Quality Criteria (U.S. EPA, 2012).

Beaches may also have classification systems that consider a number of factors in assigning an overall rating to the beach (see Other tools for public education and communication for more information on beach classification). For such systems, it is suggested that a minimum of 60 samples should be used to characterize water quality, although a greater number of samples (for example, closer to 100) provides a more precise estimate (WHO, 2009). As many beaches do not collect this number of samples yearly, water quality results from multiple bathing seasons (when no substantive change has occurred in the watershed) can be combined.

When developing sampling programs, defining the purpose of the monitoring program (for example, to determine water quality trends, to investigate spatial distribution of pollutants, to detect specific hazards) will help determine the types and frequency of sampling that is needed. This may include collecting samples to characterize event-driven episodes of pollution that may affect recreational waters (for example, immediately following periods of heavy rainfall or at times of greatest swimmer activity). Information collected during an areas' EHSS will also aid in identifying key factors that should be considered during sampling program design. Detailed information on the design and implementation of recreational water monitoring programs are outside the scope of this document but are described elsewhere (Bartram and Rees, 2000; U.S. EPA, 2010).

Less frequent monitoring may be possible under certain circumstances, such as at beaches in remote locations or in areas where primary contact recreational activities are not a regular occurrence. Beaches that have historically demonstrated water quality results well below the guideline values through relatively intensive monitoring and the use of an EHSS may also be able to reduce their sampling frequency to help ease the burden of monitoring (Bartram and Rees, 2000; WHO, 2003, 2021). Thus, if it can be determined that a recreational water area is of consistently good microbiological quality, does not have any obvious sources of fecal contamination and is not considered to present a significant risk to the health and safety of its users, monitoring may be reduced to a frequency that is sufficient to verify that the conditions have not deteriorated (for example, once a month). If the water quality deteriorates, an investigation into the cause is recommended and it may be necessary to return to an increased sampling frequency. It may also be acceptable to reduce monitoring frequencies for recreational water areas that consistently demonstrate poor water quality results, but only where appropriate management actions are taken to discourage recreational use and the risks are clearly communicated to the public.

Location of microbiological sampling

Most bodies of water used for recreational purposes are not completely homogeneous with respect to their microbiological properties. In recreational water evaluations, the purpose of sampling is to obtain aliquots that are as representative as possible of microbiological quality of the area. A single water sample provides a quantitative estimate of the indicator bacteria present at a particular site and time. Multiple samples may be needed to provide a more accurate estimate of the water quality during each sampling event (Whitman and Nevers, 2004; U.S. EPA, 2005a, 2010). The number of discrete sampling locations included during a sampling event should be based on the beach characteristics as well as the fecal sources identified as part of the EHSS. However, as the total number of samples increases, the more representative the data will be of the overall water quality.

Sampling sites should be chosen to be representative of the water quality encountered throughout the entire swimming area. This should include points of greatest swimmer activity, as well as peripheral points subject to external fecal contamination. Stormwater, sewage or river outlets can give certain sections of a body of water microbiological qualities that are very different from those of the water body at large. If there are distinct areas that are highly influenced by a pollution source and they can be delineated from the rest of the beach area, it is possible to sample these areas separately. At some longer beaches, sources of fecal pollution can vary significantly along the length of the beach (Edge et al., 2010). The degree of heterogeneity in a water area can also be affected by rainfall, wind direction and velocity, currents and tides or the presence of physical barriers, such as sandbars, natural or artificial wave breaks and piers. Further general guidance on microbiological sampling can be found in the Microbiological Sampling and Analysis guideline technical document (Health Canada, in publication) and detailed sampling plan guidance has been published elsewhere (U.S. EPA, 2010).

The depth at which samples are collected can have a significant effect on the resulting estimates of water quality ('depth' refers to the vertical distance in the water extending from the bottom of the water to the surface). Where the water is very shallow, disturbances of the foreshore sand and sediment caused by wave swash and swimmer activity can result in the resuspension of fecal indicator microorganisms (Whitman and Nevers, 2003; Vogel et al., 2016; Palmer et al., 2020). This resuspension may inflate microbiological estimates but not necessarily reflect an increase in bather risk if pathogens are not also present in the sediments. Where the water is deeper, this effect has less influence on water quality measurements. In contrast, deeper waters are relatively more exposed to offshore fecal sources than shallower waters (U.S. EPA, 2005a). Adult chest depth (approximately 1.2 to 1.5 m from the bottom) has historically been the most common sampling depth, although newer epidemiological studies have also used waist depth (approximately 1 m). Traditionally, this has been considered to represent the depth of greatest swimmer activity and the location nearest to the point of head immersion, which would be indicative of the risk associated with accidentally swallowing water. However, sampling at shallower depths (ankle or knee depth, approximately 0.15 to 0.5 m from the bottom) may be more representative of water quality encountered by young children playing at the water's edge. Epidemiological studies have typically found that only samples collected at depths greater then knee depth show a mathematical relationship between indicator organism density and swimmer illnesses (U.S. EPA, 2010). It is suggested that a reasonable but still conservative approach to monitoring may be to sample at waist depth (U.S. EPA, 2010). The sample depth (or depths) selected for an individual beach should be determined by the local or regional authority in order to obtain the best information for their particular recreational water area. However, if more than 1 sampling depth is included in the monitoring plan, all samples collected at a specific depth should be analyzed as a single group (for example, for calculating the geometric mean) in order to improve the precision of the data.

Composite sampling

Composite sampling provides a way to increase the area covered under a beach monitoring program, while potentially minimizing the costs associated with analysis. Composite sampling involves the collection of multiple samples from across a stretch of beach, combining them into 1 large composite, and then analyzing a subsample of the resulting mixture. There are some challenges with the use of this technique. Increased sampling is required initially to validate whether composite sampling will be feasible at a given area. The area must be characterized to identify hot spots (sampling points having continuously poor water quality) that can disrupt the analysis. Some level of statistical knowledge is required to analyze the data. Nevertheless, investigations have suggested that, if properly conducted, composite sampling can be used to make water quality decisions with a degree of accuracy comparable to that achieved by analyzing the samples individually and averaging the results (Kinzelman et al., 2006; Bertke, 2007; Reicherts and Emerson, 2010). Further information on composite sampling can be found in the Guidelines for Canadian Recreational Water Quality – Microbiological Sampling and Analysis technical document (Health Canada, in publication).

Fecal pollution source tracking methods

Fecal source tracking can be used to supplement the monitoring and assessment tools that are already in place in recreational areas. Understanding the fecal sources can help to assess potential public health risks, as sources of human and ruminant fecal contamination have been shown to be of greater concern than other animal sources (see Quantitative microbial risk assessment below). It can also help target appropriate risk management barriers, which can both reduce beach notifications and help prevent waterborne disease outbreaks.

Fecal source tracking initiatives should be designed to answer a specific question and should be based on the analysis of the available data, including bacteriological sampling, EHSS results and local knowledge. In order to conduct fecal source tracking, it is important to have a good understanding of the nature of the fecal pollution problem. The EHSS is a particularly useful tool for helping recreational water area operators, service providers and local authorities identify the potential sources of fecal contamination that are relevant to their recreational water area. It is also important to have the necessary expertise for designing and carrying out the study. This may include individuals from the public (for example, government scientists) or private (for example, university researchers) sectors with knowledge of fecal source tracking methodologies.

If fecal source tracking is being considered, there is a toolbox of methods available. Many of the available methods are not standardized. However, they are well described in the scientific literature. A number of methods have been used successfully in recreational water settings to identify unexpected fecal pollution sources, to verify information from other lines of evidence, to resolve local beach closure problems involving limited fecal sources and to break down large source tracking problems into more manageable studies (Kinzelman and McLellan, 2009; Converse et al., 2012; Edge et al., 2018; Edge et al., 2021). Fecal source tracking is also being used to aid in beach management decisions (Government of Alberta, 2019).

The choice of methods will depend on the question that needs to be answered, the suspected fecal sources and the expertise of the researchers involved. The methods selected may differ depending on whether the study only needs to differentiate human from non-human sources, or whether the fecal pollution attribution needs to be broken down into more categories (for instance, human, cattle, wildlife, birds) or linked to human illnesses.

Fecal source tracking in recreational water areas often focuses on identifying sources with known human-pathogen contributing potential (for instance, human and ruminant feces), as even minor contributions from human sewage (for example, 10% to 20% of the E. coli concentration) is sufficient to drive bather risk (Schoen and Ashbolt, 2010). Other animal markers may aid in clarifying observed or expected fecal sources but their relationship to potential disease impacts has not been clearly established (Schoen and Ashbolt, 2010). It should be noted that fecal source tracking methods may not be able to identify all of the sources contributing fecal material to the watershed and the recreational water area. Also, although markers are considered host-specific, studies have reported some cross-reactivity with species other than the intended target, generally in fewer samples and at lower concentrations than found in the target species (Nguyen et al., 2018; Staley et al., 2018b).

When designing a fecal source tracking study, a tiered approach should be considered. A tiered approach utilizes the currently available information on the watershed and recreational area (for example, fecal indicator bacteria data, land use information, sanitary infrastructure conditions) to help determine fecal sources before instituting more complex chemical and microbiological source tracking methods. Any fecal source tracking assessment should also use a toolbox approach based on multiple lines of evidence to identify fecal pollution sources. Additional information on the tiered approach is available elsewhere (Griffith et al., 2013). Further guidance on designing fecal source tracking studies can be found in publications from the U.S. EPA (2005b, 2019a,b), the Southern California Coastal Water Research Project (Griffith et al., 2013) and the US Geological Survey (Stoeckel, 2005).

If chemical and microbiological methods are needed in a recreational area, a variety of methods are available. These are described in the following sections.

Chemical methods

Chemical methods of analysis are based on the detection of chemical compounds known to be present in fecal material as a result of human activities, either through consumption and/or metabolism and the subsequent excretion in feces or via disposal as sewage wastes. Numerous chemical compounds have been investigated as potential markers for human sources of fecal pollution. Artificial sweeteners, caffeine, detergents, fluorescent whitening agents, fragrance materials, fecal sterols, fecal stanols, pharmaceuticals and personal care products have all been proposed as markers of fecal pollution from sewage treatment plants (Glassmeyer et al., 2005; Tran et al., 2015; Devane et al., 2019). Chemical tracers such as smoke or dyes have been used to confirm suspected sources of contamination, such as wastewater outfalls and wastewater infrastructure cross-connection issues. Some advantages to using chemical markers include a shorter analysis time than for many microbial methods, low detection limits and ease of analysis (Haack et al., 2009). Potential drawbacks may include differing fates in the environment for chemical markers compared to microorganisms (Glassmeyer et al., 2005), lack of any consistent relationship with illness for risk modelling (Napier et al., 2018), non-fecal sources of some chemical markers (Tran et al., 2015) and costs. However, chemical markers can be used as part of multiple lines of evidence and a toolbox approach to understanding fecal sources.

Microbial methods

Microbial source tracking (MST) methods are based on the premise that certain fecal microorganisms are strongly associated with specific hosts and that particular attributes of these host-associated microorganisms can be used to determine fecal sources (Harwood et al., 2014). MST methods can be divided into library-dependent and library-independent methods. Library-dependent methods were more widely used in early MST studies, whereas in recent investigations, library-independent methods are used almost exclusively.

Library-dependent methods establish a reference library of characteristics of individual fecal indicator bacteria isolates obtained from known fecal sources and then compare these characteristics to those from "unknown" water sample isolates. For example, a library could be a database of antibiotic resistance profiles or DNA fingerprints of E. coli isolates obtained from animal feces and municipal wastewater effluent (Wiggins, 1996; Dombek et al., 2000; Carson et al., 2001; Edge and Hill, 2007). The similarity of the profiles or fingerprints of E. coli isolates obtained from recreational waters ("unknowns") can then be compared with the profiles or fingerprints in the library ("knowns") to make statistical inferences about the source of the waterborne E. coli isolates. There are numerous drawbacks to this type of method. They require large reference libraries for comparison to unknowns (smaller libraries with fewer than 1,000 biotypes tend to mislead in associations), are prone to misclassification of fecal sources (especially when the library size is limited) and the libraries are not transferable between locations (Griffith et al., 2003; Stoeckel et al., 2004). They are also labour intensive and can have long wait times for results. These drawbacks have generally led to a discontinuation of library-dependent methods that are based on collecting isolates for fecal indicator bacteria. However, there has been some investigation into using high-throughput DNA sequence analyses such as high-density microarrays (Dubinsky et al., 2012, 2016) and next-generation sequencing results for MST (Staley et al., 2018a; Unno et al., 2018). These methods are considered library-dependent methods and are being investigated as part of the MST toolbox.

Library-independent methods are now more widely reported in the scientific literature. They involve detecting host-specific DNA markers or host-specific organisms (bacteria or viruses) to identify the sources of fecal contamination in the water. Most library-independent methods rely on PCR methods (quantitative PCR, digital PCR or, in early studies, end-point PCR) to detect the markers or organisms of interest. Examples of host-specific markers include toxin genes (Khatib et al., 2002, 2003), genes for virulence factors (Scott et al., 2005) and highly conserved DNA sequences (Bernhard and Field, 2000a; Johnston et al., 2010). In particular, human-specific markers within the 16S rDNA of the genus Bacteroides are widely used (Bernhard and Field, 2000b; Layton et al., 2006; Kildare et al., 2007; Okabe et al., 2007; Ahmed et al., 2009; Shanks et al., 2009; Green et al., 2014; Mayer et al., 2018). Animal host-specific DNA markers have also been developed, including avian, ruminant and various pet markers (Bernhard and Fields, 2000a; Kildare et al., 2007; Lu et al., 2008; Shanks et al., 2008; Weidhaas et al., 2010; Green et al., 2012). The host-specific viruses most commonly researched are human adenovirus, human polyomaviruses, pepper mild mottle viruses and the phage crAssphage (McQuaig et al., 2009; Ahmed et al., 2010; Wong et al., 2012; Rusiñol et al., 2014; Symonds et al., 2016; Farkas et al., 2019). Although there can be some geographic variability in host-specific markers and host-specific organisms, these methods have been applied successfully to MST studies in recreational waters worldwide (Boehm et al., 2003; Bower et al., 2005; Noble et al., 2006; Hughes et al., 2017; Cao et al., 2018; Nguyen et al., 2018; Staley et al., 2018b).

There are advantages and drawbacks to library-independent methods. On the positive side, these methods are less labour intensive than library-dependent methods and therefore are easier and less expensive to conduct. Some of the best host-specific markers (for example, HF183 for human sources) have been shown to be transferrable across regions (Mayer et al., 2018) and may be related to bather illness (Boehm et al., 2015; Cao et al., 2018; Boehm et al., 2018; Boehm and Soller, 2020), although this relationship has not been consistently reported (Napier et al., 2017). Some human-specific markers (for example, crAssphage) also occur at high concentrations in raw sewage (Farkas et al., 2019; Korajkic et al., 2020) and decay more slowly than other genetic markers (Ahmed et al., 2019), which makes them useful for fecal source tracking. One of the main drawbacks of library-independent methods is the need to develop source specific markers that are applicable across watersheds and that have a minimal amount of cross-reactivity with non-target fecal materials.

Quantitative microbial risk assessment

Quantitative microbial risk assessment (QMRA) is used to estimate the potential health risks associated with a specific exposure scenario. Assessments use water quality information, assumptions on exposure conditions and dose-response models for specific pathogens as inputs to provide risk estimates. In recreational settings, QMRA has been used to better understand the relative potential health impacts from human pathogens, as well as to support decisions about health risk in water quality management plans. QMRA studies require a significant amount of data on the recreational water area and a high level of technical expertise to conduct properly. These are considerable limitations to their more widespread use.

Estimating health risks at beach sites

QMRA has been used in research studies to investigate the estimated risks from various pathogens at beach sites (Boehm et al., 2018; Federigi et al., 2019; Sunger et al., 2019). The pathogens most often included are enteric viruses (for example, noroviruses, human adenoviruses), enteric protozoa (for example, Cryptosporidium, Giardia) and enteric bacteria (for example, Campylobacter, Salmonella). QMRA studies are often conducted as an alternative to epidemiological studies. Although epidemiological studies can directly investigate health risks to the public, they are expensive and labour intensive. QMRA studies can also predict risks to lower levels than can be identified using epidemiological studies. However, QMRA studies are only as good as the information that is used to support their development. They involve numerous assumptions that may need to be validated for the site of interest.

Some researchers have conducted QMRA studies in parallel with epidemiological studies to compare the health risk outcomes. For example, in a study investigating wet weather impacts on surfer health in southern California, similar gastrointestinal (GI) impacts were estimated when comparing the QMRA analysis to the epidemiological study results (15 GI per 1,000 recreation events vs 12 excess GI per 1,000 recreational events, respectively) (Soller et al., 2017). Another paired QMRA and epidemiological study in Chicago, investigating secondary contact activities, reported approximately an order of magnitude difference in the health risk from the 2 approaches (Rijal et al., 2011; Dorevitch et al., 2012). QMRA methods have also been used to reanalyze the epidemiological study data from Boquerón beach in Puerto Rico where no links to human health could be identified. The QMRA predicted 2 to 3 illnesses per 1,000 recreators, well below the level that would be detectable by the epidemiological study (Soller et al., 2016). Although conducting QMRA investigations requires a high degree of scientific expertise, these studies highlight the usefulness of QMRA for estimating human health risks in a recreational water quality setting.

Comparing health risks from various fecal sources

Using QMRA, researchers have also investigated the relative risks from different fecal sources, including human sewage sources, stormwater runoff, bird contamination issues and agricultural fecal inputs. This research is the basis for recommending the development of alternative water quality guideline values when appropriate (for example, based on site-specific risk assessments).

Human sources of fecal material (for example, municipal wastewater, septic systems, other swimmers at the beach) pose the greatest risk to human health as they are the sources most likely to contain human pathogens. Most studies have reported that the enteric viruses, specifically norovirus, pose the greatest risk to swimmer's health in recreational waters (Schoen and Ashbolt, 2010; Soller et al., 2010a; Dufour et al., 2012; McBride et al., 2013; Eregno et al., 2016; Vergara et al., 2016). Other fecal sources (for example, agricultural and wildlife) can contain pathogens of human health concern, but the impacts are more variable. A study of the potential risks from stormwater runoff containing only animal fecal sources estimated the risk to human health from cattle, pig and chicken manure to range from 30 to 180, from 35 to 65 and from 25 to 6 000 times lower, respectively, than the potential risks from municipal wastewater at similar levels of E. coli and enterococci (Soller et al., 2015). Fresh fecal matter from cattle has been estimated to present a risk of illness similar to municipal wastewater, but chicken, pig and gull feces were lower risk (Soller et al., 2010b). Researchers also estimated at least a 1 log lower health risk from gull feces than from sewage, assuming the same enterococci concentrations (Schoen and Ashbolt, 2010). In recreational sites, enterococci from waterfowl feces can predominate but may represent a significantly lower human health risk compared to sites that have sewage contamination (even at low levels) (Schoen and Ashbolt, 2010). Risk modelling has shown that when less than 10% to 30% of the enterococci present in recreational water is from human sources, the potential risk to human health may be significantly lower than indicated by the bacteriological indicator guideline value (Schoen and Ashbolt, 2010; Soller et al., 2014). Although non-human fecal sources are usually lower risk, there are times when animal fecal material can contain higher levels of human pathogens, for example, E. coli O157:H7 in calves (Soller et al., 2015).

In general, the predominant fecal source at a recreational site may not be the dominant health risk. Some studies have combined QMRA methods with data from human-specific fecal markers (for example, HF183) to estimate health risks from specific pathogens, as well as to estimate threshold concentrations for the human-specific markers that correspond to the health risk levels associated with the 2012 U.S. EPA recreational water quality criteria for E. coli and enterococci (Brown et al., 2017; Boehm et al., 2018; Boehm and Soller, 2020). Other human-specific fecal source tracking markers could also potentially be used. However, further research is needed before guidelines could be developed.

QMRA in water quality management plans

Although implementation of QMRA requires a high degree of scientific knowledge, it has been used to support site-specific recreational water quality management plans. A pilot project at an Australian beach used sanitary survey information, combined with a QMRA approach, to design a site-specific recreational water quality management program (Ashbolt et al., 2010). In Canada, the Government of Alberta has used published QMRA data on comparative risks to implement fecal source tracking as part of their updated safe beach protocol (Government of Alberta, 2019). The Guidelines for Canadian Recreational Water Quality - Indicators of Fecal Contamination technical document uses QMRA study results as support for developing alternative recreational criteria on a site-specific basis (Health Canada, 2023). The U.S. EPA, in its most recent recreational water quality criteria, allows for the development of site-specific water quality objectives using QMRA models when non-sewage source(s) drive the health risk (U.S. EPA, 2012).

Predictive water quality models

Predictive water quality modelling uses mathematical approaches (for example, linear regression equations, artificial intelligence tools) to predict whether a water quality target (for example, E. coli or enterococci guideline values) may be exceeded. Approaches can range in complexity. The overall goal is to use the predictive modelling results as part of a recreational water quality management plan. The modelling informs public health decisions regarding the suitability of the water quality for recreational activities.

Using models to predict fecal indicator bacteria concentrations can overcome some of the limitations of current monitoring approaches, such as the lag times associated with obtaining culture-based fecal indicator bacteria results and less than daily bacteriological sampling frequencies (WHO, 2003; U.S. EPA, 2012, 2016). Predictive models are designed to make same-day predictions, including on weekends, when many recreational areas are not being monitored. Models can also be automated, so that predictions are generated daily and automatically sent to beach managers (Searcy et al., 2018). It should be noted that not all beaches are good candidates for the use of predictive modelling in their recreational water quality management plans (MOE, 2012; U.S. EPA, 2016). Beaches that hardly ever exceed guideline values or beaches where the water quality is known to remain constant over extended periods of time may not benefit from predictive tools. Also, in order for predictive tools to work, a set of variables must be available for use in modelling the water quality with a reasonable degree of accuracy. A list of common variables used for modelling can be found in U.S. EPA (2016). Recreational areas that are subject to a wide or frequently changing set of conditions and disturbances that are not predictable are not good candidates for modelling.

Predictive models have been developed and validated using data from various water- and weather-related parameters (for example, rainfall, wave height, wind direction, turbidity, fecal indicator counts). Examples of such models include SwimCast (Olyphant and Pfister, 2005; Lake County Health Department, 2010), NowCast (Francy and Darner, 2007; Francy et al., 2013a; Francy et al., 2013b) and Virtual Beach (Frick et al., 2008; Mednick, 2012; Cyterski et al., 2013; Neet et al., 2015), although numerous other examples have also been published (Nevers et al., 2009; Lawrence, 2012; Chan et al., 2013; Francy et al., 2013b; Jones et al., 2013; Gonzalez and Noble, 2014; Brooks et al., 2016; He et al., 2016; U.S. EPA, 2016; Searcy et al., 2018). In many cases, predictive models have been shown to have a degree of accuracy comparable to, or greater than, traditional fecal bacteria beach monitoring for providing correct and timely beach management decisions. Models are not static, however, and ongoing evaluation and improvements to the models are necessary (Searcy et al., 2018). U.S. EPA (2016) outlines a 6-step process for developing and using predictive modelling at a beach site.

There are a number of challenges associated with using predictive tools. A significant level of technical expertise is required to develop the models, to analyze and interpret the data, and to maintain and re-evaluate the models. Moreover, as mentioned earlier, models may not work in all areas. Modellers use historical data to develop the mathematical equations that describe the relationships between different variables. Therefore, data on the recreational area must be available. Data from well-designed monitoring programs, representative of the range of conditions, will be most useful for developing predictive models. The models need to be validated against monitoring data to ensure they are providing accurate estimates. If these challenges can be addressed, beach operators, service providers or responsible authorities looking for an additional tool with which to potentially improve the timeliness of their water quality decisions may wish to investigate this approach.

Monitoring for cyanobacteria and their toxins

Appropriate monitoring programs for cyanobacteria blooms and their toxins provide early warning information to inform users of potential health risks. Both planktonic cyanobacteria and benthic cyanobacteria can cause illnesses in human and animals. Not all rivers and lakes used for recreational activities need to be monitored for cyanobacteria or their toxins. Instead, responsible authorities should use criteria to help evaluate the risk of bloom formation in order to identify the water bodies that are at greater risk. The types of recreational activities that are taking place in the area and the level of exposure of individuals in the event of a cyanobacteria bloom formation also need to be considered. This information can then be used to prioritize areas that should be monitored, to determine a monitoring approach (for example, what to monitor, how often) and to develop an action plan for responding to a bloom event. Further guidance on cyanobacteria and their toxins can be found in the Guidelines for Canadian Recreational Water Quality - Cyanobacteria and Their Toxins technical document (Health Canada, 2022a).

Other monitoring

Other water quality parameters (for example, colour, clarity, oil/grease film) related to the physical or aesthetic characteristics of a recreational water body and its surrounding environment have links to the health and safety of recreational water users and thus may be included in a monitoring program. Guideline values or aesthetic objectives have been specified for these parameters where necessary. Further information can be found in the Guidelines for Canadian Recreational Water Quality - Physical, Aesthetic and Chemical Characteristics technical document (Health Canada, 2022b).

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