Officials in Minnesota made a worrying discovery in a lake outside St. Paul, Minnesota, of zebra mussel larvae, one of the most pervasive threats to the waters of the Great Lakes region.

What's happening?

Officials with the Minnesota Department of Natural Resources (MDNR) confirmed there are zebra mussel larvae in Tanners Lake in Landfall, Minn., according to a report from Pioneer Press. Samples showed 12 zebra mussel larvae, called veligers, present in the water.

"While the DNR has not found adult zebra mussels in Tanners Lake, the presence of veligers suggests reproducing zebra mussel populations," officials said in a statement. Due to their presence, Tanners Lake is now listed as "infested with zebra mussels," per the department.

Minnesota state law requires boaters, anglers, and those who own waterfront property to follow strict guidelines to prevent the spread of zebra mussels, regardless of whether a lake has an infestation.

Why are zebra mussels important?

Zebra mussels are an invasive species that can spread quickly. The MDNR notes that females can produce 100,000 to 500,000 eggs per year. After their veligers (fertilized eggs) form shells, they can attach themselves to surfaces, forming dense beds that can reach tens of thousands in a single square yard. They were first recorded in the Great Lakes region in 1988, believed to have been introduced through contaminated cargo ship ballast water. 

The zebra mussels have caused major disruptions to the ecosystem, outcompeting native mussels and other species for resources and interfering with natural aquatic plant growth. For people, they can clog water intakes for power plants, encrust boats and other equipment, and cut swimmers' and pets' feet when they're attached to docks and rafts.

Minnesota isn't the only state dealing with the headaches caused by the invasive species. Officials in Iowa recently discovered zebra mussels in the Des Moines River, part of their spread westward over the past few decades. 

What's being done about zebra mussels?

The MDNR encourages people to report the presence of zebra mussels in any body of water, regardless of whether there's a known infestation or not. They should also follow the department's guidelines on cleaning boats, properly disposing of bait, and drying vessels for 21 days before moving from one body of water to another.

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