My young son, Eli, and I ran to the river to see what was splashing. We arrived to see the flashing caudal fin of a fat goldfish spawning in the lush outgrowth of arrowleaf and elodea. This was a happy sound. The whole scene was bittersweet and happy.
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What’s going on with the fish in the Chicago river system? Sam Dennison, fisheries biologist for the Metropolitan Water Reclamation District (MWRD), has been surveying fish populations in our river system for more than 20 years. Systematic assays of fish communities are reliable indicators of stream quality. Numbers, quantities alone, are one part of the assay. “Over the past ten years we’ve seen a ten- to hundredfold increase in fish populations,” says Dennison. “Of course we were starting from a pretty low baseline. But these kinds of increases are certain evidence of improvement in fish habitat.”
It’s been almost ten years since our waste-treatment plants stopped chlorinating sewage effluent that is dumped into the North Channel at Howard Street. Since then alien species of carp, exotic, runaway goldfish, and their hybrids have been thriving. And the system has grudgingly allowed an increase in species diversity.
“White sucker. Dorsal and pectoral fin rot, hemorrhaging, 188 grams. This is what a lot of these fish are up against in this type of environment–constantly fighting off an abundance of bacterial and viral infections.” That’s part of what limits diversity, the inability of many species to thrive in an unpredictable eutrophic stew.
