Great Lakes Water Levels Continue to Drop

Bill's Blog

Sunset at South Haven, Michigan on Saturday September 18, 2021

What goes up must come down, they say. In the last month, all five of the Great Lakes have see water levels drop – anywhere from one to six inches. The level of the lakes usually falls a bit in late summer and fall. The drop in water levels of the Great Lakes has been pretty remarkable.

Graphs of the Water Level of Each of the Great Lakes

The water level of Lake Superior is down 1″ in the last month, but down a whopping 11″ in the last year. Each inch of water on Lake Superior represents 551 billion gallons, so that’s a loss of 6.06 TRILLION gallons in just one year. So far this year, Marquette has had 77% of average precipitation, Duluth has had 78% of average precipitation and International Falls MN has had just 61% of average precipitation. The water level of Lake Superior is now one inch lower than the long-term monthly average for September. The lake is down 14″ from the highest level reached in 2019.

The St. Marys River drains Lake Superior, moving water down into Lake Huron. That river has a below average flow for the first time in years. The flow on Saturday was 69,300 cubic feet per second, compared to an average flow of 89,900 cfs That means less water coming into Lake Michigan/Huron.

The water level of Lake Michigan-Huron is down 3″ in the lasts month and down 16″ in the last year, a very substantial drop. An inch of water on Lake Huron represents 400 billion gallons and an inch of water on Lake Michigan represents 390 billion gallons. So that 16″ drop is a loss of 12,6 TRILLION gallons. Much of West Michigan has seen below average precipitation this year. Grand Rapids has had 89% of average precipitation and Holland just 71% of average precipitation. Lake Michigan/Huron is still 16″ above the September average level, but 17″ below the highest September level set in 1986 (anyone remember the “Flood of 86”).

Water levels of Great Lakes rivers and mostly not too far away from average. The flow on the Grand River in Grand Rapids early Sunday AM is 1,650 cfs, compared to an average September flow of 1,500 cfs. The Kalamazoo River at Comstock has a flow of 523 cfs compared to an average flow of 576 cfs. The Muskegon River at Croton has a flow of 1,430 cfs – average is 1,180 cfs. The Saginaw River at Bay City has a flow of 2,210 cfs compared to an average flow of 2,030 cfs. Finally, the Fox River at Green Bay WI has a flow of 2,270 cfs compared to an average flow of 2,380 cfs.

The water level of Lake Erie dropped an impressive 6″ in the last month. The lake is down 7″ year-to-year, but is still 18″ above the September average level. The lake is 9″ below the highest level set in 2019.

Lake Ontario is down 2″ in the last month and down 2″ in the last year. The lake is only 2″ above the average September level and it’s 24″ below the highest level ever reached – that was in 1947.

Lake St. Clair is down 5″ in the last month and down 11″ in the last year. The lake is still 19″ above the September average water level

The Detroit River at Detroit has a flow of 233,000 cubic feet per second, compared an average September flow of 208,000 cubic feet per second. With a higher than average amount of water exiting Lake Michigan/Huron and a low amount of water entering Lake Michigan/Huron, it’s likely the water level will continue to (very gradually) continue to go down during the fall and winter months.

I haven’t double-checked my math and it’s late, but I get a preliminary drop of 19.88 trillion gallons of water in the Great Lakes in the last year…add in Lake St. Clair and you’re probably a touch over 20 trillion gallons. I don’t know what an inch of water works out to in gallons on Lake St. Clair.

Weatherwise – one more sunny, warm September day…then we get clouds and showers Monday, Tuesday and Wednesday (lake effect rain showers on Wed.). The coolest air so far this season will be with us for the middle of the week.

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