Lake Nokomis Biomanipulation Project

Controlling bottom-feeders to control phosphorus
Project Status: 
Completed
Year Completed: 
2013
About this project: 

The Lake Nokomis bio-manipulation project aims to reduce algae in Lake Nokomis by adjusting fish populations and reducing bottom-feeding fish that stir up the lake bottom. 

Lake Nokomis is considered impaired for its nutrient content, algae content and lack of water transparency. Bottom-feeding fish -- primarily black bullheads and bluegill sunfish -- are one of a variety of causes for these nutrient pollutions issues (carp were also a major cause, but were substantially removed in 2001). A 2008 fish survey in the lake found high numbers of the black bullheads and bluegill sunfish. 

To combat these populations, the District targeted and removed adult black bullheads the lake. It also stocked walleye, which prey on bluegill sunfish and young black bullheads. 

Background

Lake Nokomis, a 201-acre lake located in south Minneapolis, has been heavily impacted by nutrient pollution. From 2000-2001, MCWD implemented a project to reduce the nutrient loading into Lake Nokomis. The project included 4 main steps:

  • installing three structures adjacent to Lake Nokomis to reduce phosphorus pollution into the lake
  • public education on the effects of phosphorus to lakes from lawn fertilizer, pet waste and other runoff
  • applying alum to the lake in order to bind up the phosphorus in the water and settle it to the lake bottom
  • remove the carp in the lake

The project was successful at reducing nutrient loading into Lake Nokomis, but did not completely address the internal loading of nutrients in the lake. A 2008 fish survey conducted by Blue Water Science concluded that one of the many internal sources that may be contributing to the nutrient impairment in Lake Nokomis is the bottom-feeding fish populations in Lake Nokomis. Carp have been known to be a significant source contributing to nutrient pollution in lakes, so they were removed in 2001. The fish survey in 2008 concluded that carp were in low densities, but that there were high numbers of black bullhead and bluegill sunfish.  Bullhead and bluegill sunfish have been known to deplete zooplankton in the water column as well as feed off the bottom of lakes. Their high numbers in Lake Nokomis suggest a significant fish source contributing to the elevated phosphorus concentrations.

Water Quality Specialist Kelly Dooley presents on the project:

Project featured on WCCO Radio