Invasive species starry stonewort confirmed in Stearns, Meeker county lakes

The Minnesota Department of Natural Resources has confirmed the presence of starry stonewort (Nitellopsis obtusa) in Lake Koronis and Mud Lake, connected to Koronis, in Stearns and Meeker counties. This is the first confirmed case of this invasive species in Minnesota.

Starry stonewort was first discovered in the U.S. in the St. Lawrence River in 1978 and has spread into lakes in the northeastern U.S. Starry stonewort was also confirmed in Wisconsin in 2014 and has been reported in Michigan lakes for more than a decade.

Lake Koronis property owners contacted DNR fisheries staff and expressed concern about abundant aquatic vegetation. DNR staff investigated and found starry stonewort in 53 acres of Lake Koronis. The plant is widely distributed in high densities in the southeast bay near the public water access off Highway 55. It is also growing outside the bay extending into the main basin, the northeast side of basin and into Mud Lake.

Starry stonewort are grass-like algae that may produce dense mats, which could interfere with use of the lake. The invasive plant also may choke out native plants and possibly alter habitat for young fish.

The invasive species was likely spread by lake users who transported fragments of the plant from an infested body of water. Because starry stonewort is widely distributed and well established in the southeast bay of Lake Koronis and has spread into the main basin, rapid response treatments such as hand removal or herbicide applications to try to remove the species would not be effective.

The DNR has surveyed many of the lakes within a 10-mile radius of Lake Koronis and Mud Lake, so far no other lakes have been found to be infested with starry stonewort. Staff will continue to determine the extent of the infestation and review management options.

The DNR reminds boaters and anglers to follow Minnesota laws to prevent the spread of aquatic invasive species:

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