Starry stonewort, an invasive species of macro algae, has been confirmed in Lake Winnibigoshish in Itasca and Cass counties, Moose Lake in Beltrami County and Rice Lake in Stearns County.  

Starry stonewort confirmed in Lake Winnibigoshish

According to the Minnesota Department of Natural Resources, 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 indicate it has also been there for several years. Rice Lake is connected to Lake Koronis and Mud Lake, where starry stonewort was first confirmed in Minnesota in August 2015.

“Since it was first confirmed in Minnesota, people are becoming more aware of how to identify starry stonewort and are bringing it to our attention,” said Heidi Wolf, DNR invasive species unit supervisor. “It is important for people to contact the DNR if they suspect they’ve found starry stonewort or any other aquatic invasive species.”

Lake Winnibigoshish is a popular 88-square-mile lake that is fed by and also flows into the Mississippi River. The DNR is investigating whether starry stonewort has spread into the river and other downstream lakes.

DNR invasive species specialists have confirmed starry stonewort extensively along the western and northwestern shores of Lake Winnibigoshish, including a public access. Because the infestation is widespread, current treatment options are limited, with efforts focusing on preventing spread within the lake and to other lakes.

Moose Lake is the fourth Beltrami County lake in which starry stonewort has been confirmed. Dense mats of starry stonewort are present across a wide range of the lake. Infestation is extensive, limiting current treatment options and putting the focus on preventing spread within the lake and to other lakes.

DNR invasive species specialists confirmed starry stonewort around the southwest public access of Rice Lake. A more extensive search is being conducted to determine the extent of the infestation and potential for treatment.

The new findings and details are consistent with some of the challenges in identifying starry stonewort. The DNR has recently investigated reports of starry stonewort that have turned out to be false.

“The telltale 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 later in the 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.”

DNR staff are collaborating with partners on an extensive, coordinated expansion of the search for starry stonewort. Meanwhile, aggressive treatment of isolated infestations on Turtle Lake and Upper Red Lake began last week, and treatment options are being discussed for Cass Lake, also in Beltrami County.

Starry stonewort are grass-like macro algae that may produce dense mats, which could interfere with use of the lake. The invasive algae also may choke out native plants. It is typically spread by lake users who transport fragments of the plant from an infested body of water.

These new infestations remind boaters and anglers to follow Minnesota laws to prevent the spread of aquatic invasive species:

• Clean aquatic plants and animals from watercraft, 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 watercraft.
• Dispose of unwanted bait in the trash.

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