“What we’re seeing is there’s less chance for that stratified layer to break down, because the temperature gradient between the top and bottom is that much stronger than we’ve had in the past,” said Alan Steinman, a research professor at Grand Valley State University’s water resource institute. “The chances of the bottom layers going anoxic, where there’s no dissolved oxygen at all, is much more likely.”

Fishermen in the greater Chicago area who spoke with the Tribune said they have yet to see an impact on Lake Michigan’s fish populations.

But that doesn’t mean they won’t in the future, according to Steinman.

“The lake is experiencing considerable pressure and is certainly operating in a different way than even 20 years ago,” he said.

Toxic blue-green algae blooms

Deep below the surface, lake stratification has other effects. Anoxic water releases sedimented phosphorus at the bottom of the lake. Phosphorus fuels toxic blue-green algae blooms.

It’s unlikely that Chicagoans will see blooms pooling on Lake Michigan’s surface, according to Steinman. Trillions of invasive quagga mussels blanket the lakebed, filtering through the water and decreasing phosphorus.

But in shallow Lake Erie, blue-green algae blooms are increasing, according to NOAA. Erie is more susceptible to warming because of its depth.

The toxins can harm humans and animals if ingested, taint coastlines and affect businesses dependent on the lake.

“These blue-green algae blooms aesthetically, you know, are terrible. So there’s an economic cost associated with that,” Steinman said.

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