Starry Stonewart found in Thunder Lake in Cass County

The Minnesota Department of Natural Resources has confirmed the invasive algae starry stonewort in Thunder Lake, near Remer in Cass County. 

DNR staff conducting a survey of algae in Thunder Lake found starry stonewort. Funding for this research was provided by the Minnesota Environment and Natural Resources Trust Fund as recommended by the Legislative-Citizen Commission on Minnesota Resources.

Follow-up surveys are being conducted to determine the extent of starry stonewort distribution in Thunder Lake. If surveys confirm that starry stonewort is in localized areas of the lake, removal in those areas might be pursued. Such a response could include hand pulling, herbicide applications and other methods as appropriate.

Starry stonewort has never been eradicated from any U.S. lake or river, but treatment or careful removal can help reduce the risk of spread and relieve associated nuisance impacts on water-related recreational activities. Early detection is key to effective management.

Starry stonewort has now been confirmed in 23 water bodies in Minnesota. It was first confirmed in Minnesota in 2015.

In late summer and early fall, starry stonewort’s small white star-shaped bulbils become more visible, making it easier to distinguish from other aquatic plants. Information on how to identify starry stonewort can be found on the DNR’s website (mndnr.gov/Invasives/AquaticPlants/StarryStonewort). If people think they’ve found starry stonewort or any other invasive species new to a lake or river, they should report it to the DNR by contacting their area invasive species specialist (mndnr.gov/Invasives/AIS/Contacts.html).

Starry stonewort is an algae that looks like native aquatic plants and can form dense mats, which can interfere with recreational uses of a lake and compete with native plants. It is most likely spread when fragments have not been properly cleaned from trailered boats, personal watercraft, docks, boat lifts, anchors or other water-related equipment. 

Whether or not a lake has any invasive species, Minnesota law requires people to:

• Clean watercraft, trailers and equipment to remove aquatic plants and prohibited invasive species.
• Drain all water and leave drain plugs out during transport.
• Dispose of unwanted bait in the trash.
• Never release bait, plants or aquarium pets into Minnesota waters.
• Dry docks, lifts and rafts for 21 days before moving them from one waterbody to another.

These additional steps reduce the risk of spreading aquatic invasive species:

• Decontaminate watercraft and equipment – find free stations on the courtesy decontamination page of the DNR website (mndnr.gov/Decon).
• Spray with high-pressure water or rinse with very hot water (120 degrees for at least two minutes or 140 degrees for at least 10 seconds).
• Dry watercraft and equipment for at least five days before using in another water body.

More information is available on the aquatic invasive species page of the DNR website (mndnr.gov/AIS).