Great Lakes–St. Lawrence River Water Levels
Volume 24, Number 9

September 2016

PDF Version (458 KB)

August Brings Most Great Lakes Wetter Supplies

All lakes saw near average or wetter supplies during the month of August, after several months of relatively wet conditions in Lake Superior and dry conditions for the rest of the lakes. This resulted in below average declines in levels for Lakes Michigan–Huron, Erie and Ontario, while Lake Superior’s level stayed the same through the month, when on average it rises slightly.

  • The monthly mean water level of Lake Superior was 17 cm above its period-of-record (1918–2015) average in August and 2 cm higher than August 2015.
  • Lake Michigan–Huron’s mean level in August was 27 cm above average and 10 cm higher than last year’s August level.
  • Lake Erie’s mean monthly level was 21 cm above average and 16 cm lower than August 2015.
  • Lake Ontario was 4 cm below its August average and 27 cm lower than the same time last year.
  • The wetter conditions in the Great Lakes extended into the St. Lawrence River basin with levels at Montreal Harbour showing a temporary rise with heavy rain mid-month, however levels remained below average due to the previous dry conditions.

Although Lake Superior once again saw above-average water supplies from its basin, these were offset by above-average outflow from the lake resulting in the lake level remaining about the same through August. On average (1918–2015) Lake Superior rises 1 cm. Lake Michigan–Huron fell 3 cm in August, slightly less than the average decline of 4 cm, with the near average water supply from the lake basin supplemented with the above-average inflow from Lake Superior. Lake Erie’s level fell 7 cm, slightly less than its average 8 cm fall for August. After dry conditions seen through the summer months, August brought Lake Ontario slightly above-average supplies, resulting in the lake declining 8 cm, considerably less than its average decline of 14 cm.


Great Lakes Water Level Information:
August 2016 Monthly Mean Level
LakeCompared to
Monthly Average
Compared to
One Year Ago
Superior17 cm above2 cm above
Michigan–Huron27 cm above10 cm above
St. Clair31 cm above2 cm below
Erie21 cm above16 cm below
Ontario4 cm below27 cm below


Great Lakes Water Level Information:
Beginning-of-September 2016 Level
LakeCompared to
Compared to
One Year Ago
Superior16 cm above1 cm above
Michigan–Huron28 cm above10 cm above
St. Clair39 cm above4 cm above
Erie24 cm above9 cm below
Ontario2 cm below20 cm below


Beginning-of-September Lake Levels

Lake Superior’s beginning-of-September level was 16 cm above average (1918–2015), 1 cm above last year’s and the highest it has been since 1996. Lake Michigan–Huron’s beginning-of-September level was 28 cm above average, 10 cm higher than last year and the highest it has been since 1997. Lake Erie was 24 cm above average at the beginning of September, but 9 cm lower than the same time last year. Lake Ontario’s level at the start of September was 2 cm below average and 20 cm below this time last year, but has been this low as recently as 2012. At the beginning of September, all of the lakes were at least 50 cm above their chart datum level (for more information on chart datum see the July 2016 edition of LEVELnews).

Lake Level Outlook

Relative to their beginning-of-month levels, and assuming average water supply conditions, all the lakes are expected to enter their seasonal fall decline as summer draws to a close. 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.


August Precipitation over the Great LakesFootnote 1
Great Lakes Basin138%
Lake Superior125%
Lake Michigan–Huron146%
Lake Erie
(including Lake St. Clair)
Lake Ontario132%


August Outflows from the Great LakesFootnote 1
Lake Superior129%
Lake Michigan–Huron106%
Lake Erie107%
Lake Ontario101%


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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