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

Volume 26, Number 10

Above-average water supplies in September

Water supplies to all the Great Lakes were above average for all the Great Lakes for September based on preliminary estimates. Despite the above-average water supplies the level of Lake Ontario was below average for the first time since the beginning of January 2017 while all the other Great Lake levels remained well above average. September monthly mean levels ranged from 1 cm below to 49 cm above their period-of-record monthly averages (1918–2017), and beginning-of-October levels ranged from 4 cm below to 50 cm above their period-of-record averages. The beginning-of-October levels for the lakes ranged from 30 cm below to 8 cm above those seen a year ago. The water levels in the lower St. Lawrence River were near or above average due to continued above average outflow from Lake Ontario and varied outflow from the Ottawa River.

September monthly lake levels

All the Great Lakes, except Lake Ontario, had above average monthly mean water levels in September. Lake Erie continued to be well above average, and the highest above average of the Great Lakes, while Lake Ontario fell below its average monthly mean water level for the first time since December 2016.

  • Lake Superior was 16 cm above its period-of-record (1918–2017) September monthly mean water level and 10 cm below its value in September 2017.
  • Lake Michigan–Huron’s monthly mean level in September was 43 cm above average and 1 cm higher than last September’s level.
  • Lake Erie’s monthly mean level was 49 cm above average and 8 cm above the level of the previous September. Lake Erie’s level was the 5th highest September mean level on record and the highest it has been for the month since 1997.
  • Lake Ontario’s September monthly mean level was 1 cm below average and 35 cm lower than September 2017.
Great Lakes water level information:
September 2018 monthly mean level
Lake Compared to monthly average (1918-2017) Compared to one year ago
Superior 16 cm above  10 cm below
Michigan-Huron 43 cm above 1 cm above
St. Clair 53 cm above  4 cm above
Erie 49 cm above  8 cm above
Ontario  1 cm below 35 cm below

Lake level changes

Above average outflows from all of the lakes offset wet supplies to varying degrees in each of the lakes, resulting in varied water level changes over the month of September.

  • Lake Superior levels rose 4 cm through September, when on average (1918–2017) it falls 1 cm, as above-average outflows could not offset above-average water supplies.
  • Lake Michigan–Huron’s above-average water supplies were more than offset by the above-average outflows for the month, resulting in its level falling 8 cm over September when on average it falls by 6 cm.
  • Lake Erie’s level fell only half its average, falling 5 cm when its average fall is 10 cm during the month.
  • Above-average water supplies to Lake Ontario continued to be offset by above-average outflows resulting in its level falling 19 cm, 5 cm more than its average fall of 14 cm.

Beginning-of-October lake levels

All the Great Lakes beginning-of-October levels were above average, except for Lake Ontario, but only Lake Erie was above its level when compared to the same time last year.

  • Lake Superior’s beginning-of-October level was 17 cm above average (1918–2017), but 11 cm below the level at the same time in 2017.
  • Lake Michigan–Huron’s beginning-of-October level was 41 cm above average and the same level as last year.
  • Lake Erie was 50 cm above average at the beginning of October, 8 cm higher than the same time last year and the highest it has been since 1997.
  • Lake Ontario’s level at the start of October was 4 cm below average and 30 cm lower than the water levels last year.
  • At the beginning of October, all of the lakes were at least 44 cm above their chart datum level.
Great Lakes water level information:
beginning-of-October 2018 level
Lake Compared to beginning-of-month average (1918-2017) Compared to one year ago
Superior 17 cm above 11 cm below
Michigan-Huron 41 cm above Same
St. Clair 56 cm above  5 cm above
Erie 50 cm above  8 cm above
Ontario  4 cm below 30 cm below
September precipitation over the Great Lakes a,b
Lake %
Great Lakes Basin 89%
Lake Superior 100%
Lake Michigan-Huron 83%
Lake Erie
(including Lake St. Clair)
Lake Ontario 86%
September outflows from the Great Lakes a
Lake %
Lake Superior 112%
Lake Michigan-Huron 111%
Lake Erie 114%
Lake Ontario 114%

a As a percentage of September long-term average.
b United States Army Corps of Engineers

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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