Illinois e-News Release

Friday, Aug. 14, 2026

SPRINGFIELD – Invasive carp sampling crews removed several hundred small silver carp from the Marseilles Pool of the Illinois River, about 80 miles from Lake Michigan, on Thursday and Friday during routine intensive monitoring of the upper river.

The fish ranged in size from about 4 to 6 inches long, and the discovery marks the first time invasive carp of this size have been found this far upriver since the monitoring program began in 2010.

The location indicates a spawning event may have occurred further upriver or in one of the tributaries that feed into the Illinois River. Flood pulses and water temperatures this summer created conditions that have been conducive to carp spawning.

Crews are now ramping up additional monitoring in the upper river and tributaries to gather more information that will allow them to assess the scope and significance of the discovery. Studying the microchemistry of the captured fish will also allow experts to determine more about their origin.

They also are implementing intensive electrofishing in backwater habitats favored by juvenile invasive carp to further evaluate the extent of this reproductive event in the Marseilles Pool and will increase monitoring efforts in the Dresden Island Pool – about 50 miles from Lake Michigan – as a precaution. Contract commercial fishing for adult invasive carp will resume in September in the Starved Rock, Marseilles and Dresden Island Pools once water temperatures cool enough for these removal efforts to be effective.

Silver carp require flowing water for reproduction as their semi-buoyant eggs need to remain suspended until hatching. Silver carp eggs float downriver for miles through their early life stages before reaching juvenile size.

Fish biologists consider invasive carp populations to be established when multiple life stages of young and adult invasive carp are present. For the Illinois River, intensive multi-agency monitoring over the past 16 years has indicated established invasive carp populations in the lower 240 miles, from the Peoria pool southward toward the confluence with the Mississippi River. North of the Peoria pool, the Starved Rock, Marselles and Dresden Island pools are known to have adult invasive carp but not multiple life stages of young.

Great Lakes partners – including the Illinois Department of Natural Resources – work together as the Invasive Carp Regional Coordinating Committee and invest heavily in early detection monitoring and rapid response preparedness to prevent invasive carp from proliferating in new areas. On the Illinois River, a detection that indicates a change in the status or distribution of invasive carp triggers specific protocols that partners have planned and practice regularly in advance.

During the past 16 years, partners have been able to hold the line on the adult population front for silver and bighead carp within the Dresden Island Pool.

Monitoring crews are made up of fish biologists and other experts from the State of Illinois, Illinois Natural History Survey, U.S. Fish and Wildlife Service, U.S. Geological Survey and U.S. Army Corps of Engineers. Commercial fishers and processors also play an indispensable role in broader efforts to keep invasive carp out of the Great Lakes and manage infestations in other parts of the Mississippi River basin where invasive carp originally established.

The monitoring program employs a statistically robust, multi-habitat, multi-gear, random sampling approach designed to detect shifts in fish abundance and community composition. The program includes consistent and standardized monitoring on all pools of the Illinois River and the Chicago area waterway using mini fyke nets, standard fyke nets, direct-current boat electrofishing, small and large hoop nets, and electrified dozer trawls. Monitoring results are reported weekly online.