Carp wreak havoc on marsh habitat

In fall 2001, one carp was identified in the lakes during the Illinois Department of Natural Resources’ (IDNR) annual fisheries survey of Hennepin and Hopper lakes. IDNR did not record the presence of common carp again until spring 2006.

Common carp are voracious feeders and mature fast. Once in a marsh system, they quickly overpopulate and destroy native habitat.

Recognizing a decline in the health of the lakes, The Wetlands Initiative in 2007 invited scientists from the University of Minnesota, led by Dr. Peter Sorensen, to lead a mark-and-recapture study to estimate the size and age of the carp population and to project its future growth.

Based on this research, TWI ecologists estimated that the population increased from less than 1 lb/acre in 2002 to more than 250 lbs/acre in 2007. Despite efforts to reduce the population by commercial and volunteer fishing efforts, the population was still estimated to be 400-500/lbs/acre by spring 2009.

While the carp population was growing, Dr. Gary Sullivan, TWI’s senior restoration ecologist, surveyed the decrease in the number and diversity of aquatic plant life in the lakes. By 2009, less than 4% of the lake area contained any live aquatic vegetation (e.g., cattails, white water lily, and Southern naiad)—a sharp decline from 2003 when more than 90% of the lake area was covered with aquatic plants.

Many submersed species that are only found in high-quality aquatic habitat are no longer present at all, including Sago pondweed, wild celery, nodding longleaf, and duck potato.  

Aquatic vegetation is critical to maintaining the health of the entire ecosystem. Plants anchor the food web, provide shelter for invertebrates, fish and birds, help maintain ideal water temperature, and maintain water clarity by holding down sediment.

Duck and geese populations have also declined. By 2007, IDNR estimated that the waterfowl population had dropped by more than 90%, according to the department’s fall aerial surveys. 

For more information visit:

Press Release on Hennepin & Hopper Lakes Rehabilitation

Illinois Department of Natural Resources Carp Fact Sheet

U.S. Geological Survey Carp Fact Sheet

Illinois State Museum “Harvesting the River” Exhibit

Journal article (PDF): Effects of a rapidly increasing population of common carp on vegetative cover and waterfowl in a recently restored Midwestern shallow lake, by Przemyslaw G. Bajer, Gary Sullivan, and Peter W. Sorensen, from Hydrobiologia, 2009, Vol. 632, No. 1, pp. 235-245.