LEBANON — Maine and New Hampshire officials will measure and monitor the presence of an invasive aquatic plant that can grow up to seven feet in one growing season.

European naiad has recently been confirmed to be in a 1,040-acre impoundment comprised of Northeast, Milton and Town House ponds within the Salmon Falls River that separates the two states. The Salmon Falls River has shorelines in Acton and Lebanon.

The presence of European naiad, sometimes called European water nymph, was confirmed in the three ponds within the river in September, according to the Maine Department of Environmental Protection.

There are two forms of naiad native to Maine, but European naiad is not one of them.

Able to overtake native lake habitats by shading and outcompeting ecologically valuable aquatic plants, European naiad grows from an annual seed into sevenfoot long plants, according to Maine DEP biologist John McPhedron. A one-acre infestation can generate tens of millions of seeds per season. Dense infestations can alter water chemistry and oxygen levels.

The Maine DEP has been working with the New Hampshire Department of Environmental Services, the York County Soil and Water Conservation District and the local lake association to measure how much of the plant is present in the ponds and explore methods to halt its spread.

McPhedron said European naiad tends to grow more densely in shallow portions of a water body, outcompeting the native plants and ultimately changing the habitat.

McPhedron was on the water Tuesday, surveying the plants.

In a telephone interview from the ponds, he said so far, the most dense growth of European naiad has been found in shallow water near the northern portion of Northeast Pond. The plant doesn’t appear to be as much of a risk in deep water, he said.

The plant was discovered in a pond in Kittery several years ago. So far, there are no other infestations in Maine. The invasive plant had been documented previously in two New Hampshire water bodies, but populations declined on their own without management, according to Amy Smagula of the New Hampshire Department of Environmental Services.

“European naiad has not been a common problem species in this area, though with several new infestations documented in New Hampshire in 2015, that may be about to change,” she said in a prepared statement. “It warrants further investigation.”

Maine DEP and NH DES have distributed invasive species warning signs to be posted at boat ramps urging boaters to inspect for and remove plant debris before and after boating on the ponds. Also notified were boat ramp and other land owners, fishing tournament organizers, and fisheries and warden services from both states.

McPhedron said inspecting boats and gear is the best method to prevent infesting another water body.

— Senior Staff Writer Tammy Wells can be contacted at 324-4444 (local call in Sanford) or 282-1535, ext. 327 or twells@journaltribune.com.