CHICAGO (AP) —  The variety of fish swimming in Chicago’s waterways have increased in recent decades, which authorities attribute to a decline in pollution.

The Metropolitan Water Reclamation District reports there are nearly 60 different types of fish swimming in the Chicago and Calumet rivers, up from fewer than 10 in the 1980s.

Carp is the most frequently found species in the rivers. Among other species netted by district biologists were bluegill, catfish, largemouth bass and yellow perch.

Those fish are less tolerant of pollution than carp. Shedd Aquarium research biologist Austin Happel says the more robust and diverse population of fish is an example of how the fight to clean area rivers is paying off after decades of their use as industrial sewage canals.

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