The Maine Department of Environmental Protection says the species is European naiad and was found in the Salmon Falls River. The river has shorelines in Lebanon and Acton, Maine, and Milton, New Hampshire.

The biologists say the plant is able to overtake native lake habitats. It grows from a seed into seven-foot-long plants, and a one-acre infestation can generate tens of millions of seeds per season.

Environmental managers from the two states have distributed warning signs to be posted on boat ramps to urge boaters to inspect and remove plant debris before and after using the area where the plant is growing.