IDNR monitoring apparent natural die-off of silver carp on the Illinois River

SPRINGFIELD - Staff from the Illinois Department of Natural Resources (IDNR) are monitoring an extensive silver carp fish die-off in the Peoria pool of the Illinois River between roughly Henry and Peoria.

IDNR fisheries biologists believe the incident is naturally occurring, caused by spawning stress and rapid water chemistry changes from recent rain. No evidence of chemical contamination or pollution was observed, and no native fish species or other aquatic organisms were affected. It's unknown how many silver carp died because of the occurrence.

Silver carp are a species of invasive carp found in Illinois waterways. Invasive carp, including silver and bighead, typically spawn during periods of rising river levels and increasing water temperatures - both of which central Illinois has experienced recently.

"These environmental cues trigger spawning activity, often resulting in large numbers of fish moving and spawning at the same time," said IDNR fisheries chief Michael McClelland. "Spawning requires a significant amount of energy and can place considerable physiological stress on fish."

Deceased fish continue to flow downstream to other areas of the river. People who live near the river or recreate on it may notice unpleasant odors near affected areas as deceased fish decompose. These odors are expected following a fish mortality event and do not necessarily indicate an ongoing water quality problem. The smell should gradually diminish as river conditions improve and natural decomposition processes run their course.

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