Great Lakes water quality agreement: nutrients

A small boat travels through a bright green Lake Erie. The bright green colour is a result of high amounts of phosphorous in the water which cause algae blooms. A line of blooms follows where the boat has disrupted the slimy water.

A boat travels through a bright green Lake Erie. The bright green colour is excess algal blooms that have resulted from high amounts of phosphorus in the water.

Photo: © Joe Barber, Ohio Department of Natural Resources - Division of Wildlife.

Objective: To reduce the occurrence of toxic and nuisance algal blooms that degrade drinking water quality, impair fish spawning, and adversely impact commercial and recreational fishing, swimming, tourism and overall enjoyment of the Great Lakes.

Canada and the United States recognize the urgent need to manage phosphorus concentrations and loadings that are contributing to algae problems.

Lake Erie is the primary focus of attention within the amended GLWQA because it is currently having the most significant algal problems. It is the shallowest and most biologically productive of all the Great Lakes, leading it to be highly sensitive to changes in nutrient levels and changes in the food web. Both countries recognize that action is needed to understand and address the algae problem in Lake Erie.

Why is action on nutrients important?

Toxic and nuisance algal blooms are re-emerging as a significant threat to Lake Erie and nearshore areas of lakes Huron, Ontario and Michigan. Many of the algae varieties threaten human and wildlife health and lead to degraded aquatic habitat. Excessive algae also results in economic impacts by clogging water intakes, increasing water treatment costs, and disrupting fisheries, tourism and recreation.

The algae problem today is complex.  The causes of the resurgence in algae growth are not fully understood.  They include increased temperatures, increased penetration of light, and changes in phosphorus discharges and travel within the lakes.  Of the various factors which influence algae growth in the Great Lakes, it is the amount of phosphorus that can be controlled.  However, part of the challenge is that management approaches used in the past to reduce phosphorus discharges from sewage treatment plants and urban, rural and agricultural runoff may no longer be adequate or effective in all cases.

Resolving the algae problem in the Great Lakes will require agreement by Canada and the United States on the targets for phosphorus reduction and the development and implementation of phosphorus reduction strategies in each country.

Commitment to key activities within the 2012 Great Lakes Water Quality Agreement

  • Develop, within 3 years, binational substance objectives for phosphorus concentrations, loading targets, and loading allocations for Lake Erie;
  • Develop, within 5 years, binational phosphorus reduction strategies and domestic action plans to meet the objectives for phosphorus concentrations and loading targets in Lake Erie;
  • Assess, develop, and implement programs to reduce phosphorus loadings from urban, rural, industrial and agricultural sources. This will include proven best management practices, along with new approaches and technologies;
  • Identify priority watersheds that contribute significantly to lakewide or local algae development, and develop and implement management plans to achieve phosphorus load reduction targets and controls; 
  • Undertake and share research, monitoring and modeling necessary to establish, report on and assess the management of phosphorus and other nutrients and improve the understanding of relevant issues associated with nutrients and excessive algal blooms.

Expected outcomes

  • Reduce toxic and nuisance algal blooms that pose a threat to human and ecosystem health in the Great Lakes, particularly in Lake Erie;
  • Identify and take action in priority watersheds that contribute significantly to nearshore and lakewide algae problems.

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