If you dive into a lake, you might notice a sudden temperature change, rather than a gradual cooling as you get deeper. That’s because many lakes have two different layers during the summer. The warmer water on top does not mix with the cooler water on the bottom, until air temperatures decrease in the fall.

Diving into a lake

This stratification affects more than temperature. Because the bottom water is isolated from the air, the oxygen in bottom water has to last all summer for fish and other organisms that live in the deeper part of the lake.

But in the Great Lakes, a lot of that oxygen is getting used up by increasingly frequent algal blooms. And compounding that problem is global warming.

Val Klump
Val Klump

By the end of the century, summers in the Midwest are predicted to get warmer and last for three to six weeks longer than they do now. Val Klump of the University of Wisconsin says this could threaten life in those low-oxygen areas.

Klump: “The oxygen might last a month but can it last six weeks? Can it last two months? In Green Bay and in Wisconsin or in the Great Lakes in general, the summer period is projected to be maybe six weeks longer. Well, that would be a huge change.”

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A change that will put additional pressure on fish and other aquatic life as the climate warms.

Reporting credit: ChavoBart Digital Media.
Diving photo: Copyright protected.

More Resources
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Pollutants likely to create longest dead zone yet in Green Bay
Dead zones haunt Green Bay as manure fuels algae blooms


Bridgett Ennis

Bridgett Ennis is co-founder of ChavoBart Digital Media, an audio and video production firm with a focus on scientific and environmental media. ChavoBart Digital Media contributes original reporting, audio...