View the project story map with pictures and videos.
Benton Lake in Cologne has high levels of a nutrient called phosphorus which causes algae blooms in hot summer months. A study done by the Carver County Water Management Organization determined the high phosphorus levels in Benton Lake were primarily coming from within the lake, when carp and other rough fish disrupt lake sediments.
Common carp are an invasive rough fish that can severely impact water quality in lakes and rivers. Carp are bottom feeders, and while rooting around lake beds for bugs and other food they muddy the water and re-suspend phosphorus back into the water column. Their feeding also uproots native aquatic plants which then have a harder time re-establishing in the now muddy water. Without plants, lakes become more turbid (cloudy looking), have more frequent algae blooms and have less or sometimes no habitat for native game fish. Rough fish such as carp and bullheads make up almost all of the fish species found in Benton Lake.
Staff explored a number of options to remove carp from Benton Lake in order to improve water quality. The first option was a lake drawdown. This option was not favorable as it proved too expensive. The second option was to do a rotenone treatment. Rotenone is a piscicide: it targets fish. A licensed contractor is needed to do the treatment. Staff put together requests for proposals twice but no contractors bid on the project citing concerns about mitigating downstream impacts as a main reason. After discussions with staff from the Minnesota Aquatic Invasive Species Research Center, a third option was developed: a multi-step method to control carp populations similar to that done on Starring Lake in Eden Prairie. Research has shown this method can be as effective as a rotenone treatment. The project will consist of 1) Electro-fishing and tagging carp to estimate populations and track movements 2) removing carp through traps and seine nets, 3) stocking the lake with bluegill which eat carp eggs, and 4) potentially installing an aerator to help keep bluegill populations alive during the winter. Carver County Water Management Organization has contracted with a consultant, Carp Solutions, to carry out the project.
Tasks & timeline
The project started fall of 2017. Staff expect to continue this contract with Carp Solutions and repeat these steps as necessary for the next 2-3 years. View project story map for full tasks and timeline.
Photos below show staff checking bait and net, staff electro-fishing, and carp collected.
Once carp populations have been reduced, it is the goal that the water will become clearer which will allow for aquatic plants to grow. The lake has a healthy seed bank for aquatic plants. The aquatic plants with further root the lake sediments in place and keep both phosphorus and sediment from re-suspending into the water column. The stocked bluegills should keep the carp population in check and two carp barriers will prevent new carp from getting into Benton Lake or Meuwissen Lake.
More Information on Research
The Minnesota Aquatic Invasive Species Research Center has completed a number of research projects on behaviors, impacts and removal methods for carp. This includes nearby projects such as Starring Lake in Eden Prairie and a new project on 6 Mile creek and lakes included in its watershed.