Public access to a popular lake near Bemidji has been temporarily curtailed while the state attempts to remove a tenacious and annoying form of nonnative algae.

The Minnesota Department of Natural Resources (DNR) has temporarily closed public access to Turtle Lake while it conducts aggressive treatment on an expanse of starry stonewort that covers nearly three-fourths of an acre of the lake's surface.

Starry stonewort is a grasslike algae that can produce dense mats on the surface of a lake. They can choke out native plants, create a wall between fish and their spawning grounds, and interfere with boaters and anglers.

The public access is expected to reopen before Labor Day, the DNR said. In the meantime, a nearby resort owner has volunteered his access elsewhere along the 1,436-acre lake. Anglers fish Turtle Lake for walleye, northern pike, largemouth bass, bluegill, crappie, rock bass and perch.

Contractors are using pumps to vacuum up the vegetation and an accompanying layer of mud from the lake, known locally as Big Turtle. Fragments of the algae and the tiny star-shaped bulbils for which the plant is named can prompt new growth.

Once the cleanup is complete, a copper-based herbicide will be applied in hopes of killing the last remnants of the vegetation and bulbils.

Heidi Wolf, a DNR invasive species unit supervisor, said the cleanup is going well, but she added: "To date, starry stonewort has not been eradicated from an infested lake anywhere in the United States."

The herbicide being used to treat the lake is not harmful to fish or humans at the prescribed dosage for this project, she said.

Two other infestations of starry stonewort have been confirmed in Beltrami County, the DNR revealed last week. One is in Upper Red Lake and the other is in Cass Lake, within the Leech Lake Reservation. Treatment options are being reviewed in both cases.

The state's first known infestation was confirmed a year ago in Lake Koronis, 185 miles south of Turtle Lake.

Wolf said other Minnesota lakes may also be infested, adding that the DNR will continue to watch for the invasive weed and discuss prevention methods.

Starry stonewort is typically spread by watercraft that transport fragments from an infested body of water. The DNR urged boaters and anglers to follow Minnesota laws to prevent the spread of aquatic invasive species:

• Clean aquatic plants and animals from watercraft, trailers and equipment.

• Drain all water by removing drain plugs, and keep plugs out while transporting watercraft.

• Dispose of unwanted bait in the trash, not in the lake.