By IJC staff
Following 15 years of generally dry weather, the Great Lakes basin has experienced wetter conditions during the past four years. The four upper lakes – Superior, Huron, Michigan and Erie – are all well above average. Lakes Huron, Michigan and Erie are at their highest levels for this time of year since 1998. Lake Ontario and the St. Lawrence River were inundated with record-setting floods last year, but are now at lower levels than they were a year ago.
Water levels on the Great Lakes rise and fall in response to natural water supplies and levels change from day to day. Natural water supplies are the total inputs from rain, snow, runoff and inflows from upstream, minus evaporation from the lake surface. Outflows from lakes Superior and Ontario are regulated at dams approved by the International Joint Commission, allowing a limited degree of influence over high and low water levels. Lakes Michigan and Huron, connected by the Straits of Mackinac, rise and fall as a single lake.
Lake Superior was near the upper end of its historical range during the winter, but did not rise as much as usual in April. The level as of May 3, 2018, is about 1 inch (3 centimeters) below its level from a year ago. The IJC’s International Lake Superior Board of Control expects Superior to remain above its long-term average over the next six months, unless conditions are extremely dry. Regulated outflows from Lake Superior have been above average for the past six months and are expected to remain above average through the summer.
Water levels as of May 3 on lakes Michigan and Huron were about 3 inches (7 centimeters) above their level at the same time last year, according to the board. Levels are expected to remain above average over the next six months, even under extremely dry conditions. As of May 3, Lake Erie was about 4 inches (10 centimeters) above its level at the same time last year. It is expected to remain above average over the next six months, even if conditions are extremely dry. Strong winds can vary the level along the Lake Erie shoreline by several feet from one end of the lake to the other, causing short-term flooding and wave damage as seen along the western end of the lake on April 14-15.
Water supplies to Lake Ontario have been above average for more than a year, including record high monthly supplies in May 2017 and February 2018, and the highest-ever two and three consecutive months of supplies from April through June 2017. Regulated outflows have been extremely high throughout this period, including all-time record releases during the summer of 2017. February 2018 outflows were the highest in any February on record.
As of May 3, the Lake Ontario water level was 8.5 inches (22 cm) above average, according to the International Lake Ontario-St. Lawrence River Board, although about 16 inches (41 cm) below its level this time last year. With normal supplies, Lake Ontario is expected to fall toward average by mid-summer and remain near average through the end of the calendar year. Outflows are as high as possible without creating significant flooding in the St. Lawrence River.
Information on regulated outflows from lakes Superior and Ontario is available from the IJC’s International Lake Superior Board of Control and International Lake Ontario-St. Lawrence River Board.