A single zebra mussel was found in Lake Harriet on Sept. 8.
The adult zebra mussel was discovered on a boat cover recovered from the bottom of the lake. Park Board staff worked with the Minnesota Department of Natural Resources, the Minnehaha Creek Watershed District and contractors to conduct 67 hours of shoreline, snorkel and scuba surveys. No additional mussels have been found.
“One mussel is a question mark,” said Keegan Lund, metro area invasive species specialist with the DNR. “I think it’s realistic to say that zebra mussels could be introduced into a lake and do not successfully establish for a variety of reasons.”
He said finding one mussel in Lake Harriet means there’s a need for further monitoring.
The DNR added Lake Harriet to its infested waters list for zebra mussels. The lake can get off the list if future surveys show no zebra mussels in the lake, though Lund said that’s never happened.
Zebra mussels, first found in the Great Lakes nearly 30 years ago, cause over $1 billion in economic harm in North America each year, according to the state’s aquatic invasive species research center. They can cut swimmers’ feet, clog irrigation intakes and other pipes, outcompete native species for food and smother native mollusks.
The effects of zebra mussels will vary by lake, depending on the type of lake and the rockiness of the lake bottom, Lund said. Mussels generally need hard surfaces to settle on but can settle on plants.
He said they can have a huge impact on the power industry, clogging pipes for power plants on rivers. In Lake Harriet, the bigger impact would be ecological, Lund said.
Zebra mussels filter out large amounts of algae and could make the water more clear and clean. That could impact the lake’s food web.
Lund said the Lake Harriet zebra mussel was found by accident, after a volunteer dive group pulled some material from the lake. He said subsequent searchers “scoured that lake as well as possible.”
According to the DNR, about 1.8 percent of Minnesota’s lakes are listed as infested with zebra mussels. No mussels have been found in Lake Calhoun/Bde Maka Ska or Lake Nokomis, according to the Park Board.
The finding won’t impact public use of Lake Harriet. The Park Board, which began an invasive species-inspection program in 2012, will continue to inspect boats and watercraft entering and exiting Lake Harriet, Lake Calhoun/Bde Maka Ska and Lake Nokomis through public boat launches until Dec. 1 or when the lakes ice over.
Jeremy Barrick, the Park Board’s assistant superintendent of environmental stewardship, cautions that anglers and other lake users need to remain vigilant in stopping the spread of zebra mussels and other invasive species.
“We believe that our extensive (invasive species) program, greater public awareness and more Minnesotans following our state’s invasive species laws have helped keep our lakes free of zebra mussels up to now,” he said in a statement. “However, we also know that it may take years for an infestation to fully develop.”
State law requires boaters to clean watercraft of aquatic plants and prohibited invasive species, remove drain plugs and keep them out during transport and dispose of unwanted bait in the trash.
The Park Board recommends boaters take precautions such as spraying boats with high-pressure water, rinsing with hot water and drying for at least five days.
Visit dnr.state.mn.us/invasives/aquatic to learn more.