A reclamation project to kill and replace all the fish in Pickerel and Mud lakes began Thursday.

The Minnesota Department of Natural Resources, in conjunction with the Shell Rock River Watershed District, had sought to do the work on Monday and Tuesday. Rain has delayed the work. On Thursday, the DNR set up a command center in the gravel parking lot across Ninth Street from Wedgewood Cove Golf Club.

Today, a helicopter flew low over Pickerel Lake, dropping the chemical rotenone into the water. Law enforcement blocked U.S. Highway 69 temporarily as the helicopter made passes over the water near the roadway.

Thursday, DNR staff injected the fish-killing chemical into ditches, tributaries and inlets feeding into Pickerel Lake. Many of the waterways were reachable only by small all-terrain vehicles.

The intent of the reclamation project is to improve water quality on Pickerel Lake. A large rough fish population, mostly carp, has damaged habitat in the lake. Carp also contribute to algae blooms by stirring up sediments at the bottom of the lake.

An electric fish barrier near the outlet of Mud Lake will keep rough fish from re-entering the lake, and the barrier keeps the fish in the lake.

After the rotenone application, the DNR is not planning to remove the fish. Leaving the fish should be similar to a winter fish kill, where the fish sink and naturally decay at the bottom rather than floating. The DNR could remove some fish if there’s a high number floating near a home or public area.

The lake will be closed to public access during the rotenone application. For a few days after the application, the water will likely have a chemical odor comparable to mothballs.