The Illinois Department of Natural Resources (IDNR) is monitoring a large die-off of invasive silver carp in the Illinois River.
According to IDNR fisheries biologists, the event appears to be caused by the combined effects of spawning stress and rapid changes in water chemistry following recent rainfall. Officials reported no evidence of chemical contamination or pollution. No native fish species or other aquatic organisms have been affected.
The total number of silver carp that died has not been determined.
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Likely Triggered By Natural Forces
Silver carp are one of several invasive carp species established in Illinois waterways. Along with bighead carp, they typically spawn during periods of rising river levels and warming water temperatures. These conditions have recently occurred across central Illinois.
“These environmental cues trigger spawning activity, often resulting in large numbers of fish moving and spawning at the same time,” IDNR Fisheries Chief Michael McClelland, said “Spawning requires a significant amount of energy and can place considerable physiological stress on fish.”
Biologists believe that physiological stress, combined with rapidly changing water conditions, led to the mortality event.
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Dead Fish Moving Downstream
Dead silver carp are continuing to drift downstream, meaning residents encounter fish carcasses beyond the initial affected area.
IDNR said for locals to expect unpleasant odors as the fish decompose. These smells are a normal and do not necessarily indicate an ongoing water quality issue. The agency expects the odors to lessen naturally as river conditions stabilize and decomposition progresses.
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Monitoring Continues
IDNR staff continue to monitor conditions throughout the affected stretch of the Illinois River and are gathering information on the extent of the die-off.
The department encourages anyone who observes large numbers of dead fish of the same species in an Illinois waterway to report the incident to IDNR.
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