What’s in the Illinois River and Is It Safe to Swim In?

Written by Samantha Stanich
Updated: August 13, 2023
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The Illinois River begins at the Mississippi River and has a length of about 273 miles.

As a main principal tributary of the Mississippi River, the Illinois River is known for its abundant fishing opportunities and stunning shorelines. The 273 miles (439 km) long river is entirely in the state of Illinois, offering recreational waters and shorelines to the state’s residents. Swimming in the Illinois River isn’t recommended due to the high bacteria and algae in the water. What does this mean for what is in the Illinois River? There are still a variety of fish that call the river home, and plenty of recreational fun to be had on the Midwest river.

The Illinois River has abundant fishing opportunities along its stunning shoreline. Fish in the waters include:

  • Black Crappie
  • Blue Gill
  • Brown Bullhead
  • Channel Catfish
  • Largemouth Bass
  • Sauger
  • Walleye
  • White Bass
  • White Crappie

Read on to dive into the Illinois River and find out what animals call the river home. We will also find out where you can swim in the Midwest waters!

Can You Swim In the Illinois River?

Illinois River in late summer when the water is low.

Image: Wandering Introvert, Shutterstock

©Wandering Introvert/Shutterstock.com

No, it is advised to not swim in the river due to the high bacteria and algae in the water.

Why Can’t You Swim In the Illinois River?

The Illinois River flows lazily by bluffs at Buffalo Rock State Park on a summer's evening

The river is an important part of the Great Loop, the circumnavigation of Eastern North America by water.

©Hank Erdmann/Shutterstock.com

The river is polluted with phosphorus, and reports show that 80% of nitrate pollution comes from agriculture. The other pollution is traced to sources like wastewater treatment facilities. The pollution decreases water transparency, allows green-blue algae to grow, and does have detrimental impacts on lake species.

The Illinois River sees pollution due to altered water flows for agriculture. This changes the timing, volume, and often the direction of drainage systems. Agriculture is the most obvious example since 75% of the state’s total land use is devoted to the industry. The changing of water flows affects water quality, particularly through the discharge of pollution and sediment into waterways, and even the alteration of water temperature.

A red barge ships cargo down the Illinois River near Ottawa, Illinois. Aerial photograph via drone.

The river now forms the basis for the Illinois Waterway. This extended the river’s capabilities for commercial shipping.

©Steve Gadomski/Shutterstock.com

Recreation On the Illinois River

Though swimming is not advised, there are other ways to enjoy the river. Fishing is a popular pastime as is boating, canoeing, and kayaking to explore the scenic waterways.

Visitors can also make use of the many hiking trails found in the surrounding areas. Birdwatching is another popular activity due to the diverse range of avian species that call this region home. There are also several campsites and RV parks along the river’s shoreline. So, if you want to enjoy the Midwest region and all the outdoors have to offer, you have your choice of activities!

What Is In the Illinois River?

The river is home to a diverse population of fish species. These include catfish, bass, crappie, and walleye to name a few. The river is a beautiful destination for anglers and fishing enthusiasts. The most common catches in the river are bass, crappie, bluegill, and sunfish.

Prime fishing spots include downstream pools located below the five separate dams because they offer calm waters. South of the Starved Rock Dam to the Mississippi River sees a lot of species of fish as well as below Marseilles and Dresden dams. The tailwaters of the river are also an angler’s favorite spot.


Big Bass Large mouth - Fishing on lake with blue sky at dawn, sunrise

These freshwater fish are highly prized by sport fishers and anglers for their large size and willingness to put up a fight.

©Ryno Botha/Shutterstock.com

There are multiple species of bass in the Illinois River. They include:

White and yellow bass are one of the only bass species that are native to the river. Though white bass are larger and more abundant in the waters. Both species thrive in parts of the water where there is a current. They are most common in the river’s tailwaters, and behind large rocks or other obstructions. The best day to fish for both of these fish is in the early morning or late evening, preferably any time when the air is cool. The fish find deeper water during hot days. The best months for white and yellow bass fishing are May to August.

Anglers usually find trophy-size largemouth bass in the Illinois River. These fish make their homes in the main channel and lake habitats along the main channel. Largemouth bass also hide in underwater stumps, weed beds, and other vegetation where they can camouflage to stalk prey. May, June, and September are the best months for finding a monstrous largemouth. If you find yourself fishing the Illinois River in the summer, try to get out on the waters early in the morning.

Smallmouth bass are also plentiful, but not as common as largemouth bass. Anglers find them in the river north of Peoria during the early morning or late evening hours when the temperature is cool. Smallmouths also hide near rocky shorelines.


Walleye are among the most popular gamefish in North America.

These popular gamefish are nocturnal. Their unique eye structures give them strong sight even in dark waters.


These fish can be monstrous but aren’t as abundant as other fish species in the river. However, they are fun for fishermen to find! Walleye in the Illinois River can reach over 24 inches! Anglers find these gamefish during the spring. However, since the tailwaters don’t freeze over during the winter due to the currents, they also find walleyes in colder months.


These fish greatly range in size from a species that is less than an inch long to one that can grow up to 15 feet in length and 660 pounds!

©KT photo/Shutterstock.com

If you want to catch catfish in the Illinois River, you may want to try the side channels that branch from the waters. The best time to catch these fish is when the waters flood into the lowland timbers. When the river’s waters are high, catfish move into the channels in search of food. You can find the fish throughout the river wherever there is underwater cover such as submerged stumps, fallen trees, and log jams. They also like to stay along the banks where they can find deep holes to hide.

The Illinois River’s average catfish weighs between two and 10 pounds. There have been catches of 15 pounds, and even flathead catfish weighing in at 30 pounds! Anglers catch these beauties in July as other gamefish fishing begins to slump and continue to catch them through September. And, it doesn’t matter if it is night or day to find catfish.

Fishing on the Illinois River is for any experience and any level. There is something for everyone!

Where Is the Illinois River Located On a Map?

The river flows through the Midwest, originating from the confluence of Des Plaines and Kankakee Rivers. This is near Channahaon, Ill. The 273 miles of the Illinois River merge into the Mississippi River at Grafton, Illinois.

The river stretches across Illinois, running through LaSalle, Peoria, Fulton, and Mason counties just to name a few, before it enters Missouri.

The photo featured at the top of this post is © Eddie J. Rodriquez/Shutterstock.com

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