Adler Planetarium

A couple more inches of rain a year or a few degrees warmer may not seem like a big deal. But these weather changes, already underway in the Midwest, could be devastating for the health of Lake Michigan. When city sewers overflow, rainwater runs into nearby waterways, carrying pollutants with it. As heavy rainstorms become more frequent, more gasoline, trash, fertilizers, pesticides, and other contaminants will degrade Chicago's water quality and harm fish and other aquatic wildlife. And the force of the stormwater flowing into the lake or rivers can erode shorelines and disrupt fish spawning, development, and migration.

Warmer-than-normal lake temperatures could also wreak havoc on the food web. Higher water temperatures block nutrients from spreading throughout the lake, making it hard for organisms at the bottom of the food chain to find food. As a result, everything from tiny crustaceans to large predatory fish are left with less to eat. And because warmer water has less oxygen, rising temperatures could leave fish without the oxygen they need to grow and reproduce. Long-term increases in water temperature can even cause a massive die-off of fish.

Unusually high temperatures, especially during winter months, can also lead to low lake levels. Winter ice cover slows down evaporation, but when large portions of the lake remain ice-free, more water is lost than spring and summer rainfall can replace.