What happens to the Chicago River in the winter?

Blog 4
February 1, 2021

World Wetlands Day is February 2, so we’re thinking all about local aquatic habitats and the animals that live in them. We reached out to our friends at the Friends of the Chicago River to ask them what happens under the ice in the Chicago River!

J Quail Headshot

John Quail, Director of Policy and Conservation

MJ picture

Maggie Jones, Manager of Conservation Programs

The Chicago River system is a unique and important aspect of our local ecological landscape. The Friends of the Chicago River has focused on improving this habitat since their founding in 1979, they have made huge headway in making this habitat more livable for both aquatic organisms and the humans who live around it.

Let’s check in with John Quail and Maggie Jones, Director of Policy and Conservation and Manager of Conservation Programs, to understand what this important waterway is like during the extreme Chicago winter!

The Chicago River doesn’t completely freeze. Certain sections along the North Branch, for instance, freeze almost every year. If the surface of the main stem in downtown Chicago freezes, the city operates an ice breaker to free up the waterway for safety purposes.

On the surface it may appear the water has stopped moving, but underneath the ice the river continues to flow. Water temperatures are cooler under the ice and warmer near the bottom. If the river is covered in ice and snow it will be darker under the surface than during an open water sunny day.

While their activity level slows down, fishes continue to swim and live beneath the ice. They are more likely to be closer to the bottom where the water temperature is warmer. Animals that eat those fish often will migrate or enter into a type of hibernation. An example are osprey. They head to warmer climates in the fall to ensure they can find their favorite food – fish – more easily. In the spring they join us in northern Illinois again.

Wildlife often stay huddled in their habitat, and away from the wind on cold days to stay warm and preserve their energy. On warmer days you will see them be more active, much like humans. Plant life in our region has evolved with the greatly fluctuating temperatures we experience in our seasons. During the winter many plants may appear to not be healthy but they’re in a state of dormancy. Think of it as a deep sleep. When warm temperatures return they spring back to life again.

And it takes a long time for the temperature of the river to change, so even when there’s a warmer day followed by a freezing day, the temperature of the river doesn’t fluctuate.

In the winter at Friends we work on land restoration. It’s the best time of year to clear woody invasive plant species. While the ground is frozen we don’t damage the soil and wildlife isn’t as active to lessen disturbing them. In the growing season Friends conducts plant surveys at our project sites, has volunteer wildlife monitors out in the field, and also hosts litter pickups. We welcome you to visit our website in the coming months to learn more and join in.

We’re already experiencing more flash flood events. Rainfall totals in May of 2020 set a record that had just been broken the year before in 2019 (and that was broken the year before in 2018). There’s also a growing issue of when the ground is frozen and yet we have a rainfall event. When that occurs, the ground isn’t going to absorb the water which causes flooding and has impacts on sedimentation and erosion. Ideally the precipitation is in the form of snow while the ground is frozen so the water is held above ground and can slowly melt in warmer temperatures.

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