Fremont and Mills counties (Iowa DNR News) – The Iowa Department of Natural Resources (DNR) will treat Folsom, Scott B, and Lake Virginia late this summer or early fall (pending workable weather conditions) with rotenone, a botanical pesticide, to eliminate the fish populations.

Two of the lakes, Folsom and Scott B, are borrow lakes created during the construction of Interstate 29. Flooding by the Missouri River in 2019 introduced rough fish into these lakes, displacing almost all sport fish. The most recent fishery survey included common carp, silver carp, shortnose gar and black bullhead.  These injurious fish species reduce water clarity, destroy aquatic plants, and prevent the fishery from reaching its full potential.

Lake Virginia, located in Waubonsie State Park, suffered severe winter kill during the past winter. Winter kill occurs during prolonged periods of ice and snow cover that eventually depletes the oxygen from the water. Bryan Hayes, DNR fisheries management biologist, says “Surviving fish including black bullheads and common carp have gained the upper hand at Lake Virginia. The most effective method to reclaim these lakes for fishing is to eliminate the existing fish populations with a fish toxicant, rotenone; clearing the way for restocking sport fish.”

Rotenone is used world-wide and has been since the 1930s.  It is a common tool that fisheries managers use for managing sport fish and improving water quality. Rotenone is a naturally occurring compound that comes from the roots of a tropical plant in the bean family. The DNR commonly uses the commercially available formulation, 5 percent Prenfish, which has been approved for fisheries management by the U.S. Environmental Protection Agency (EPA).

The EPA has concluded that the use of rotenone for fish control does not present a risk of unreasonable adverse effects to humans or the environment. The EPA certifies all pesticides based on use according to label directions, which the DNR is equipped to fulfill these obligations.  Eliminating injurious fish species is an imperative step to achieve water quality and fishery improvements.  The three lakes will be stocked with largemouth bass, bluegill and channel catfish in the spring of 2022. Catchable-size fish are expected in the lakes as soon as 2023.