LEVELnews: Great Lakes and St. Lawrence River water levels, April 2018

Volume 26, Number 4

March dry for all Great Lakes

All the Great Lakes had dry conditions in March, after generally wet conditions through the winter. Lake Superior’s level fell much more than its average fall in March, levels on Lakes Michigan–Huron  and Ontario fell when on average they rise, and Lake Erie rose much less than its average March rise. The levels in the St. Lawrence River at Montreal fluctuated above and below average through the month, ending the month above average due to rain and snowmelt. Despite the dry conditions, all lakes remained well above average levels.

March monthly lake levels

Monthly means for all the lakes were above average by at least 25 cm in March.

  • Lake Superior was 31 cm above its period-of-record (1918–2017) March monthly mean water level and 15 cm higher than March 2017.
  • Lake Superior’s monthly-mean level was the second highest for March on record and 7 cm below the record high set in 1986.
  • Lake Michigan–Huron’s mean level in March was 46 cm above average, 23 cm higher than last March’s level and the highest since 1997.
  • Lake Erie’s mean monthly level was 60 cm above average, 21 cm above the level of the previous March and the highest it has been since 1998.
  • Lake Ontario’s March monthly mean level was 25 cm above average and 7 cm lower than the level last year.

Lake level changes

Dry conditions through March kept levels lower in all the lakes.

  • Below average water supplies and higher than average outflow resulted in Lake Superior falling 9 cm through March, a record-high fall for the month, when its average (1918–2017) fall is 1 cm.
  • Lake Michigan–Huron’s levels fell 4 cm over March, its second largest fall, when on average it rises 5 cm.
  • Lake Erie levels rose only 9 cm over March compared to its average rise of 14 cm.
  • Lake Ontario fell a record-high 7 cm over March, when on average it rises 14 cm as a result of near-record-high outflows.
Great Lakes water level information:
March 2018 monthly mean level
Lake Compared to monthly average (1918-2017) Compared to one year ago
Superior 31 cm above 15 cm above
Michigan-Huron 46 cm above 23 cm above
St. Clair 61 cm above 22 cm above
Erie 60 cm above 21 cm above
Ontario 25 cm above 7 cm below
Great Lakes water level information:
beginning-of-April 2018 level
Lake Compared to beginning-of-month average (1918-2017) Compared to one year ago
Superior 26 cm above 12 cm above
Michigan-Huron 42 cm above 18 cm above
St. Clair 51 cm above 4 cm above
Erie 54 cm above 14 cm above
Ontario 12 cm above 19 cm below

Beginning-of-April lake levels

Dry weather through the month of March brought all the Great Lake beginning-of-April levels closer to average values than the previous month and Lake Ontario’s levels fell below those seen at the same time last year.

  • Lake Superior’s beginning-of-April level was 26 cm above average (1918–2017), 12 cm above the level at this time last year and the highest it has been since 1997.
  • Lake Michigan–Huron’s beginning-of-April level was 42 cm above average, 18 cm higher than last year and the highest it has been since 1998.
  • Lake Erie was 54 cm above average at the beginning of April, 14 cm higher than its level this time last year and the highest it has been since 1998.
  • Lake Ontario’s level at the start of April was only 12 cm above average as it levels continued to approach average values from the record highs seen in May 2017. Lake Ontario’s level was also 19 cm lower than the same time last year, the first time this has happened since the beginning-of-January 2017.
  • At the beginning of April, all of the lakes were at least 29 cm above their chart datum level.

Ice conditions on lakes

A cool March and beginning of April kept ice hanging on in the Great Lakes with nearly 20% ice cover on the lakes in the week of April 9, when the average is less than 5% for this time of year. More information on Great Lakes ice conditions can be found on the Canadian Ice Service web site.

Water levels forecast

Looking ahead to spring and summer water levels, it is likely that levels in all of the Great Lakes except Lake Ontario will continue to be well above average based on their beginning-of-April levels and past conditions on the lakes (1918–2017). If conditions are dry for Lake Ontario it could fall below average levels as soon as early summer. Relative to their beginning-of-April levels and assuming average water supply conditions, all the Great Lakes are expected to rise through April. Everyone around the Great Lakes should be prepared for higher water levels due to the lakes seasonal spring level rises, as average spring water supplies are greater than those through the winter months. For a graphical representation of recent and forecasted water levels on the Great Lakes, refer to the Canadian Hydrographic Service’s monthly water levels bulletin.


March precipitation over the Great Lakes a
Lake %
Great Lakes Basin 52%
Lake Superior 28%
Lake Michigan-Huron 45%
Lake Erie
(including Lake St. Clair)
Lake Ontario 68%
March outflows from the Great Lakes a
Lake %
Lake Superior 135%
Lake Michigan-Huron 130%
Lake Erie 124%
Lake Ontario 133%

a  As a percentage of the long-term March average.
    Note: These figures are preliminary.


For more information:

Derrick Beach (Editor)
Boundary Water Issues
Meteorological Service Canada
Environment and Climate Change Canada
Burlington ON L7S 1A1
Tel.: 905-336-4714
Fax: 905-319-6939
Email: ec.LEVELnews-infoNIVEAU.ec@canada.ca

Rob Caldwell
Great Lakes-St. Lawrence Regulation Office
Meteorological Service Canada
Environment and Climate Change Canada
111 Water Street East
Cornwall ON K6H 6S2
Tel.: 613-938-5864

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