Water temperatures in the Great Lakes are running 6 to 11 degrees above average right now, setting records for mid-July on lakes Michigan, Huron, Erie and Ontario.

The shallower waters of western Lake Erie, Lake Michigan near Green Bay, and Lake Huron at Saginaw Bay are flirting with 80 degrees.

Lake Superior, the deepest lake with by far the highest volume of water, is not as warm as the other Great Lakes, but still is running over 6 degrees above average. But some water temperatures along the shore near Duluth, Minnesota; Ashland, Wisconsin; and Ontonagon, Michigan, are flirting with 70 degrees, according to analyses from the Michigan Sea Grant.

The reason for the record warm water is straightforward. There’s been an exceptionally persistent warm weather pattern across this part of the nation for much of the summer. The most anomalously warm temperatures so far in July have been over the Great Lakes into parts of eastern Canada.

Buffalo, New York, on the eastern shore of Lake Erie and known for its exceptionally snowy winters, recently set an all-time record in its nearly 150 years of taking observations, with eight straight days of temperatures that hit 90 degrees or higher. No wonder water temperatures at the Lake Erie shore set a string of daily records there.

Muskegon, Michigan, crushed its record with nine straight days of 90-degree-plus highs through July 7. Even Marquette, Michigan, sweated through a record-tying 12 straight days with highs in the 80s from late June through early July.

Less Chilly Swimming, But Less Effective Air Conditioning

The hot summer has drawn more people to Great Lakes beaches. The warmer water means more are likely swimming in the Great Lakes this summer compared to other summers with colder lake water.

Even with the record temperatures on the Great Lakes, that water is still several degrees cooler than adjacent land temperatures for much of the hottest part of this summer. That’s because it takes an enormous amount of heat to warm such large bodies of water.

The lakes serve as a natural air conditioner for residents who live nearby. For example, Buffalo has never officially hit 100 degrees, due to the cool prevailing southwest winds that come off Lake Erie.

The warmer lake water this summer means this natural air conditioner may not be quite as potent, unless stronger winds push the warmer surface water away and allow deeper, colder water to rise to the surface, a process known as upwelling.

The cooler breezes off the lakes also suppress cloud development, so that many areas downwind of the lakes experience a significantly higher percentage of sunshine than many other parts of the nation May through July.

Algal Bloom Concerns Lower

Harmful algal blooms are a rapid growth of algae that produce toxic or harmful effects on people, fish, marine mammals, birds and local economies.

Although warmer water temperatures are more favorable for the growth of the toxic blue-green algae, known as cyanobacteria, the overwhelming factor that leads to blooms is the runoff from fertilizers off farm fields that flow into the western end of shallow lakes like Lake Erie.

Fortunately, precipitation for the last 90 days ending July 14 has been well below average for the basins that drain into that portion of Lake Erie.

Only a moderate summer algal bloom is expected in western Lake Erie this summer because of the drier spring and less nutrient runoff.