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Starry stonewort introduction to Lake Superior prevented by watercraft inspectors

Oct 04, 2022 08:46AM ● By Content Editor
Photo: Minnesota Department of Natural Resources

From the Minnesota Department of Natural Resources - October 4, 2022

Vigilant DNR watercraft inspectors prevented the introduction of starry stonewort to Lake Superior, which is currently not known to be infested with the harmful invasive species.

A DNR watercraft inspector saw what appeared to be grass in the motor intake of a boat whose owner approached the Agate Bay public water access to Lake Superior in Lake County. Upon closer examination, the inspector noticed the small star-shaped bulbils that indicate starry stonewort. The boat owner said the boat had been on Bowen Lake in Cass County the previous weekend. Starry stonewort was confirmed on Bowen Lake in August. The inspector used the decontamination station on site to ensure the invasive species was removed before the boat entered Lake Superior.

“If not for the vigilance of this DNR watercraft inspector, starry stonewort would have been introduced to Lake Superior,” DNR Watercraft Inspection Program Coordinator Adam Doll said. “This incident is just one example of how the DNR, our partners, volunteers and vigilant Minnesotans work together to prevent the spread of invasives. It also reminds everyone to carefully inspect watercraft when they leave any waterbody or face a fine and the possibility of spreading invasive species to a new lake.”

Nearly 900 watercraft inspectors were hired in Minnesota this year and trained by the DNR. This included about 800 local government watercraft inspectors and 100 DNR inspectors. DNR Conservation Officers also assist with watercraft inspections statewide. Local government watercraft inspectors are funded by a portion of the $10 million Minnesota counties receive to prevent the spread of aquatic invasive species.

Starry stonewort has 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 ( 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 ( People who want to help search for starry stonewort and other invasive species can also sign up for “Starry Trek,” ( an annual statewide volunteer event coordinated by University of Minnesota Extension.

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 (
  • 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 (

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