DNR conducting aggressive treatment of Rice Lake starry stonewort

The Minnesota Department of Natural Resources access on the south side of Rice Lake in Stearns County has been temporarily closed for aggressive treatment of an isolated infestation of the invasive algae starry stonewort. 

The access is expected to reopen in about a month. The public access on the northwest corner of Rice Lake remains open, and other private accesses are also in use.

A floating curtain has been installed at the south public water access on Rice Lake to confine the affected area for treatment. Contractors will use a suction dredge to remove the vegetation and a layer of muddy substrate where starry stonewort fragments or bulbils may be present. Algae fragments and the tiny star-shaped bulbils for which the plant is named can cause new growth. After the physical removal of the vegetation and substrate, a copper-based herbicide will be applied to the area in an effort to kill any remaining vegetation or bulbils that could be left. The DNR is coordinating these management efforts with the Rice Lake Association.

As part of the DNR’s ongoing response to this relatively new invasive species, a mechanical harvester is also removing the invasive algae biomass around the Highway 55 public access on Lake Koronis, where starry stonewort was first discovered in Minnesota in August of last year. Starry stonewort has not been effectively eradicated from any lake in the United States, but treatment around accesses can limit spread to other parts of a lake and reduce the potential for transport to other lakes.

Starry stonewort are grass-like algae that may produce dense mats, which could interfere with use of the lake. The invasive algae may also compete with native plants.

The invasive algae are typically spread by lake users who transport fragments of the plant from an infested body of water. Boaters and anglers are reminded to follow Minnesota laws to prevent the spread of aquatic invasive species:

  • Clean aquatic plants and animals from watercraft, trailers and equipment.
  • Drain all water by removing drain plugs and keep drain plugs out while transporting watercraft.
  • Dispose of unwanted bait in the trash.

Some invasive species are small and difficult to see at the access. To remove or kill them, take one or more of the following precautions before moving to another body of water, especially after leaving infested waters:

  • Spray with high-pressure water.
  • Rinse with very hot water (120 degrees Fahrenheit for at least two minutes or 140 degrees Fahrenheit for at least 10 seconds).
  • Dry for at least five days.

More information about aquatic invasive species and how to report them is available on the aquatic invasive species page.