Starry stonewort, an invasive species of macro algae that can produce dense mats, which can interfere with the use of a lake and choke out native plants.

The invasive species has now been confirmed in Lake Winnibigoshish in Itasca and Cass counties, Moose Lake in Beltrami County, and Rice Lake in Stearns County.

The Minnesota Department of Natural Resources (DNR) reports that a resort owner on Moose Lake said he noticed a dense growth in the same area of the lake for several years.

DNR invasive species specialists said the extent of the spread and depth of starry stonewort in Lake Winnibigoshish indicates it has also been there for several years. Lake Winnibigoshish is a popular 88-square-mile lake that is fed by and also flows into the Mississippi River, now the DNR is investigating whether the algae has spread into the river and other downstream lakes. 

Rice Lake is connected to Lake Koronis and Mud Lake, where starry stonewort was first confirmed in Minnesota in August 2015. Specialists have confirmed the species around the southwest public access of Rice Lake, and are conducting a more extensive search to determine the full extent of the infestation. Treatment options will be decided once this is complete.

Both Lake Winnibigoshish and Moose Lake's infestation of starry stonewort is so extensive that there are limited treatment options available to the DNR. Their main concern now is to prevent the spread within the lake, as well as other lakes in the area.

"The tell tale star-shaped bulbils for which it is named typically don't appear until late in the season," said DNR invasive species specialist Tim Plude. "If people see it in June or July, they'll see what looks like heavy weed growth, and the bulbils aren't easily visible until alter int he year. They typically emerge in August and into the fall, which is why these new cases are being found now and why it's a good time for everyone to look for it."

Aggressive treatment of isolated infestations on Turtle Lake and Upper Red Lake began last week, and treatment options are being discussed for Cass Lake in Beltrami County.

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

  • CLEAN aquatic plants and animals from water craft, along with mud and debris, which may carry starry stonewort bulbils
  • DRAIN all water by removing drain plugs and keep drain plugs out while transporting water craft.
  • DISPOSE of unwanted bait in trash.