Indiana has banned the sale and distribution of two invasive aquatic plant species — starry stonewort and water soldier. Both species could hurt recreation in the state. They tend to form dense vegetation in the water that make it hard for boats to move through and can crowd out native species.

“Because of [starry stonewort’s] growth and expansion through the state, it has cost a lot of money to reduce it’s abundance,” says Eric Fischer, aquatic invasive species coordinator for the Indiana Department of Natural Resources.

Starry stonewort has spread to 20 lakes in Indiana, costing the state about $200,000 last year to eradicate. The DNR expects it will cost even more to control the species by the end of this year, roughly $250,000. Fischer says Michigan is having a much harder time — it’s been found in hundreds of lakes there.

Though water soldier hasn’t been found in Indiana yet, officials with the Indiana Department of Natural Resources say someone could accidentally introduce it into the state if it catches a ride on their boat or they plant it in their water garden. The species is currently causing trouble in the Canadian province of Ontario.

Megan Abraham is the director of the DNR’s entomology division. She says boaters can help stop the spread of these species.

“Just take some, a few minutes every time you get your boat out of the water. Check the trailer, check the boat. Make sure that you’re not moving something that you’re not meaning to move,” she says.

READ MORE: State Moves To Ban Invasive Plants Trade

Indiana is also working to ban the sale of a host of invasive plants on land. The DNR expects to hold a public meeting about the ban in early December.

Indiana Environmental reporting is supported by the Environmental Resilience Institute, an Indiana University Grand Challenge project developing Indiana-specific projections and informed responses to problems of environmental change.