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Metropolitan Water Reclamation District of Greater Chicago

The MWRD aquatic ecology team tracks the density and diversity of fish populations in the area waterways.  We use boat-mounted and backpack electrofishers, and seines to collect fish at sampling locations throughout the region. The fish are weighed, measured, identified and returned to the river. 


An electrofishing boat on a river with blue skies
The MWRD electrofishing boat on the South Branch of the Chicago River


Two workers on a boat taking notes of the size, weight and species of fish
Collected fish being weighed, measured, and identified
A person holding up a fish while on a boat prior to releasing the fish back into the river
A channel catfish about to be released back to the river


Since monitoring began in the early 1970s, we have seen dramatic improvements in species diversity, from just ten species in 1974 to 77  today. The overall fish population and size of individual fish have also increased as water quality has improved. Our studies with partners at the Shedd Aquarium have also shown that native species have increased while the number of invasive species has declined.

Fish Species Collected by the MWRD in the Chicago Area Waterway System since 1974

American eel
Banded killifish
Bigmouth shiner
Black buffalo
Black bullhead
Black crappie
Blackstripe topminnow
Bluntnose minnow
Brassy minnow
Brook silverside
Brook stickleback
Brook trout1
Brown bullhead
Brown trout
Central mudminnow
Central stoneroller
Channel catfish
Chinook salmon
Coho salmon
Creek chub
Emerald shiner
Fathead minnow
Flathead catfish
Freshwater drum
Gizzard shad
Golden shiner
Grass carp
Grass pickerel
Green sunfish
Hornyhead chub
Johnny darter
Lake trout
Largemouth bass
Largescale stoneroller

Longear sunfish
Longnose dace
Mimic shiner
Mottled sculpin
Nile tilapia
Ninespine stickleback
Northern pike
Orangespotted sunfish
Oriental weatherfish
Rainbow smelt
Rainbow trout
River carpsucker
Rock bass
Round goby
Sand shiner
Skipjack herring
Smallmouth bass
Smallmouth buffalo
Spotfin shiner
Spottail shiner
Spotted sucker
Striped bass
Tadpole madtom
Threadfin shad
Threespine stickleback
White bass
White crappie
White perch
White sucker
Yellow bass
Yellow bullhead
Yellow perch



A man holds a largeouth bass on a boat

In 2022 we collected this largemouth bass weighing over four pounds - the largest individual of this species we have collected since sampling began in 1974.