Mitchell Lake Aquatic Plant Management Guidelines

What is Growing in our Lake?

If you’ve spent any time on Mitchell Lake, you know that our lake contains a large number of aquatic plants.

  • Many people see these aquatic plants as a “weed” problem that needs to be cleaned up.
  • But what may be seen as a weedy mess may be an essential part of our lake’s ecosystem.
  • To learn more about aquatic plants check out MN DNR A guide to aquatic plants.

Algae & Weed Growth Prevention

Did you know that nutrient runoff from your yard can result in increased weed and algae growth?

What can you do?

  • Minimize or eliminate the use of fertilizer on your lawn.
  • Avoid installing hard, impervious surfaces near the lake.
  • Clean up after your pet.
  • Maintain a vegetative buffer along your shore. It not only captures nutrients but reduces erosion. Rebates are available through the City of EP, RPBCWD, and MLA.

Types of Aquatic Plants

Mitchell Lake is home to over 15 species of aquatic plants, most of which are native species, but there are also some Invasive species.

Coontail

Native Plants: Native plants function as part of a healthy aquatic ecosystem. Without aquatic plants, our lake would have fewer aquatic insects, minnows, fish, and other wildlife. When native plants interfere with boating or swimming some control may be desired. If too many aquatic plants are removed from lakeshores, fish and wildlife populations and water clarity may suffer. Examples of native aquatic plants found in Mitchell Lake include; Coontail, Filamentous algae, White Water Lilies.

Curlyleaf Pondweed

Invasive Species: Invasive species are aquatic plants not native to our waters and may cause problems. Control of these species may be done to reduce interference with boating or swimming, to reduce the risk of spread of invasive species to un-infested waterbodies, or to attempt to produce ecological benefits such as increases in native plants. Examples of invasive species found in Mitchell Lake include: Curly-leaf pondweed and Eurasian watermilfoil

Control of Aquatic Plants

Aquatic plant management has been a top priority of the Mitchell Lake Association since its inception.

The management of aquatic plants in Minnesota is regulated by Minnesota Statute, Section 103G.615, Chapter 6280 and is enforced by the Minnesota Department of Natural Resources (DNR). Aquatic plant management activities may or may not require an Aquatic Plant Management (APM) permit, based on the nature of the activity.

The Mitchell Lake Aquatic Plant Management Plan was developed by the City of Eden Prairie and the Riley Purgatory Bluff Creek Watershed District to document a long-term management approach to improve water quality, use of the lake for navigation, and the health of Mitchell Lake.

Two primary methods are used to control the aquatic plants in our lake: Mechanical control (aka. weed harvesting) and Herbicide control.

Definition:  The littoral area of the lake is the surface area of a body of water where the depth is 15 feet or less (109 acres on Mitchell Lake) and where most aquatic plants will grow.

Mechanical control

Mechanical control of aquatic vegetation typically involves cutting, pulling, raking, or otherwise removing or altering aquatic plants by physical means.

Mechanical Activity Allowed

Actions & Comments
Without a Permit

Mechanical control of submersed aquatic plants is allowed by individual property owners in an area:

  • not to extend along more than 50 feet or one-half the length of the owner’s total shoreline, whichever is less,
  • and not to exceed 2,500 sq. ft. plus the area needed to extend a channel no wider than 15 feet to open water.

These rules also allow for the mechanical control of floating-leaf aquatic plants to obtain a channel extending to open water with the provisions that the channel is:

  • no more than 15 feet wide and follows the most direct route to open water,
  • the channel is maintained by cutting or pulling,
  • and the channel remains in the same location from year to year.

Skimming of duckweed or Filamentous algae off the surface of the water is also allowed without a permit.

 Acceptable Mechanical control methods include:

  • Cutting
  • Pulling
  • Raking
  • Scuba divers
  • Mechanical harvesting
With a DNR Permit

Removal can occur as frequently as the applicant desires, however, the frequency must be approved by the DNR.

Some of the conditions of permitted mechanical control of aquatic plants include:

  • the vegetation must be immediately and permanently removed from the water;
  • the mechanical control may not exceed 50% of the total littoral area of the lake (55 acres on Mitchell Lake);
  • control methods must not change the course of the water; and
  • mechanical control for recreational access must be conducted in the same location year after year;
  • locations can vary year to year for invasive control based on pre-control surveys.
 The City of Eden Prairie typically applies for a DNR permit and contracts with a weed harvesting company 2x/year to clear the navigation paths on the lake.

  • MLA sends email notifications to property owners to allow signup for getting their shorelines harvested at the same time.
  • MLA offers a $100 rebate to have shoreline harvested in conjunction with the city-funded harvesting. Link to MLA rebate form.
  • Harvesting is similar to mowing a lawn; the plants grow back and may need to be harvested again during the growing season

Herbicide control

Herbicide control of aquatic vegetation typically involves applying a chemical to kill unwanted plants.

Herbicide Activity Allowed

Actions & Comments
Without a Permit

A permit is required for all chemical control of aquatic plants
With a DNR Permit & Variance

Herbicide control of aquatic plants must meet the following conditions:

  • treatment is limited to an area that does not exceed 15% of the littoral area of a lake (16.5 acres on Mitchell Lake).
  • Only specific pesticides that are labeled for use in aquatic sites can be used, and they must be applied according to the label instructions.

Removal can occur as frequently as the applicant desires; however, the frequency must be approved by the DNR.

 RPBCWD typically applies for DNR permit/ variance and contracts with a vendor each spring to control Curly-leaf-Pondweed, an invasive aquatic plant, that grows in our lake.

All Minnesota lakes have the same herbicide permit treatment area restrictions. However, since Mitchell lake is classified as a Natural Environment Lake, a variance is also needed to allow the use of herbicides.

  • Variances are more apt to be granted for controlling invasive species vs. native species.