The Minnesota Department of Natural Resources has confirmed the invasive algae starry stonewort in Lake Minnewaska in Pope County. This is the second new confirmation of starry stonewort in a Minnesota lake in 2017.
DNR invasive species specialists confirmed an abundant growth of starry stonewort among native aquatic plants in the narrow Lake Minnewaska marina off the main body of the lake. Additional searches are being conducted to determine whether it is anywhere beyond the marina.
Treatment options are being considered. Starry stonewort has never been eradicated from any U.S. lake, but treatment can help ease lake access and water-based recreational activities.
There are now 11 lakes in Minnesota where starry stonewort has been confirmed. Two were confirmed in 2015, seven in 2016, and two this year. It has been present in at least some of these lakes for several years, rather than being spread to many lakes in a just a year or two.
Since the first case was confirmed in 2015, all but one 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, and any suspicious plants should be reported to the DNR.
Starry stonewort is an alga that 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.