The Minnesota Department of Natural Resources has confirmed the invasive algae starry stonewort in Pleasant Lake, near Annandale in Wright County. This is the second new confirmation of starry stonewort in Minnesota in 2018. There are now 13 lakes in Minnesota where starry stonewort has been confirmed.
A DNR invasive species specialist confirmed starry stonewort when investigating a report of zebra mussels in Pleasant Lake, which turned out to be negative. Two small, dense patches of starry stonewort, 12 to 15 inches tall and covering about 4 square feet, were found in 8 to 10 feet of water, near the county-managed public access on the north side of the lake.
Staff from the DNR, Wright County and the Pleasant Lake Association are coordinating treatment. Because the patches of starry stonewort are small and deep under the surface, hand-pulling is considered the most effective treatment option in this case.
Following treatment, the access area will be carefully monitored to watch for new growth. Wright County has closed the public access until further notice. Starry stonewort has never been eradicated from any U.S. lake, but treatment can help reduce the risk of spread and provide nuisance relief for water-related recreational activities.
Since starry stonewort was first confirmed in Minnesota in 2015, most new populations have been reported in the month of August, when the telltale star-shaped bulbils are most abundant and visible. Now is the best time of year to look for it. Information on how to identify starry stonewort can be found on the DNR’s website. If people think they’ve found starry stonewort, they should report it to the DNR.
Starry stonewort is an alga that looks similar to other native plants and can form dense mats, which can interfere with use 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.
The DNR reminds boaters and anglers to follow Minnesota laws to prevent the spread of aquatic invasive species:
Clean aquatic plants and animals from watercraft;
Drain all water by removing drain plugs and keep drain plugs out while transporting watercraft; and
Dispose of unwanted bait in the trash.
Some invasive species are small and difficult to see at the access. To remove or kill them, take one or more of the following precautions before moving to another waterbody, especially after leaving infested waters:
Spray with high-pressure water.
Rinse with very hot water (120 degrees for at least two minutes or 140 degrees for at least 10 seconds).
Dry for at least five days.
Details about starry stonewort and other aquatic invasive species are available at mndnr.gov/ais.