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.

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

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

“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.