The Greenprint

Story County Conservation (SCC) and the Iowa Department of Natural Resources (DNR) are partnering to renovate the remaining fishery in Hickory Grove Lake. The DNR will treat Hickory Grove Lake later this summer (pending workable weather conditions) with rotenone, a botanical pesticide, to eliminate the remaining fish population.

An attempt was made last fall/winter to drain and dry the lake basin to rid the lake of common carp, grass carp, and black bullhead. These injurious fish species reduce water clarity, destroy aquatic plants, and prevent the fishery from reaching its full potential.

Unfortunately, common carp were observed this spring as the lake was refilling. “The most effective method to eliminate the remaining fish population is to apply rotenone to the lake basin and tributaries,” said Ben Dodd, DNR Fisheries Management Biologist.

Rotenone is used world-wide and has been since the 1930’s.  It is a common tool that fisheries managers use for managing sport fish, improving water quality, and managing endangered species.  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% 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 and final step to achieve water quality and fishery goals.

The Iowa Department of Natural Resources (DNR) and Story County Conservation (SCC) plan to start drawing down Hickory Grove Lake near Colo in early May to remove common carp. The lake will remain drained until fall.

In 2019, SCC and the DNR partnered to remove carp from Hickory Grove Lake by draining as much of the lake as possible. “Post draw-down netting suggested that we had successfully eliminated the carp,” said Ben Dodd, Iowa DNR Fisheries biologist. “Unfortunately, we observed several adult fish last week as the lake was refilling. Complete eradication of an undesirable species from a lake and its watershed is a difficult task, but we’re developing a new plan to complete the job.”

Hickory Grove Lake is a popular outdoor recreation destination in Story County, boasting a variety of activities including swimming, paddling, boating, watching wildlife and angling. Water quality in the lake has declined since the early 2000’s, due to nutrient and sediment pollution and a large population of common carp. In recent years, carp have become so abundant in Hickory Grove Lake that they eliminated aquatic plants from the lake. 

Common Carp is an invasive fish species that negatively impacts water quality and sport fish populations in Iowa lakes. They uproot and destroy aquatic plants when they feed. Sediment and nutrients are also resuspended into the water column during this process, which can lead to increased undesirable algae blooms. 

SCC and DNR recently partnered to improve water quality and recreational opportunities at Hickory Grove Lake through a variety of lake restoration practices, including shoreline deepening and armoring, revamping the beach and campground area of the park, dredging the eastern portion of the lake, making improvements to the dam and lake outlet structure, and installing a variety of fish habitat structures in the lake.

All project partners are committed to a successful lake restoration and will continue to strive for the best possible result. We intend to maximize the lake’s social, physical, and economic benefits and know that Hickory Grove Lake will again be a popular recreation destination. We thank residents and visitors for their interest and excitement in this project.

Media Contacts: Ben Dodd, Fisheries Management Biologist, Iowa Department of Natural Resources; ben.dodd@dnr.iowa.gov; 641-891-3795, or Michael Cox, Director, Story County Conservation; mcox@storycountyiowa.gov; 515-232-2516.