Iowa DNR to drain Ventura Marsh to eliminate invasive carp

The Iowa Department of Natural Resources (DNR) will begin lowering water levels in Ventura Marsh this fall to combat an invasive population of common carp. The goal is to induce a winter kill of the fish to restore the marsh and improve water quality in the adjacent Clear Lake, as nearly half of the lake’s watershed passes through the marsh.

Common carp are considered invasive because they uproot aquatic plants and stir up sediment, which degrades water quality and habitat. While fish barriers were installed in 2010 to prevent carp from entering the marsh, high rainfall in recent years has caused water levels to rise and overwhelm these barriers.

The DNR expects the project to significantly improve habitat conditions, benefiting native species and providing better opportunities for hunting and bird watching. The water levels will be maintained at a lower level through the next growing season, with refilling potentially beginning as early as fall 2027. Officials noted that excessive rainfall remains a primary challenge to the project's success.