Scot Lehigh

Weed wars

Invasive aquatic plants are choking the native life out of the region’s fresh waters

A fish’s view of a dense stand of Eurasian milfoil, a non-native invasive species. A fish’s view of a dense stand of Eurasian milfoil, a non-native invasive species. (Dennis Roberge/Maine Volunteer Lake Monitoring Program)
By Scot Lehigh
July 8, 2011

E-mail this article

Invalid E-mail address
Invalid E-mail address

Sending your article

Your article has been sent.

Text size +

ACTON, Maine

AS FANS push the July heat around, Roberta Hill is training citizen sleuths gathered in Acton’s antique town hall to identify some of Maine’s least wanted offenders.

“You see the leaded glass window, the serrated edge, and the lasagna noodle, and you’ve got it,’’ she declares.

Got what, you ask? A curly leaf pondweed; those are looks-like clues for spotting its leaves.

That weed is just one of nearly a dozen invasive aquatic plants that Maine and other Northeastern states are fighting to keep out of their lakes, ponds, and rivers.

“They are such serious invaders that once they become firmly established in a water body, they are almost impossible to eradicate,’’ says Hill, invasive plant coordinator for the Maine Volunteer Lake Monitoring Program. Others on the list of vegetative villains are European frog-bit, water chestnut, yellow floating heart, fanwort, Brazilian waterweed, hydrilla, European naiad, and several varieties of milfoil.

As non-native species, the invaders don’t face the parasites and predators that keep native flora in check, and so, when they infect a lake, they usually grow rapidly, crowding out other plant life and destroying fish habitat. Their thick growth can make it difficult to boat and hazardous to swim.

Hill and Christine Guerette of the lake monitoring organization show photographs that are enough to make a water-lover shudder. In one, for example, milfoil has transformed the surface of a Maine pond into a tangled mat of vegetation that obscures the water; it’s as though a green shag carpet has been laid down.

When it comes to battling the invaders, there’s no silver bullet, says Guerette. Sunlight-blocking mats can impede their growth, but they hurt other plant life as well. Divers, sometimes aided by suction tubes, can remove the alien plants. But those labor-intensive methods are expensive. In Vermont, where Lake Fairlee has had a Eurasian milfoil problem for more than 15 years, annual costs for the 457-acre body of water have sometimes exceeded $100,000.

With some invaders, there’s a biological approach. Weevils, for example, like to munch on non-native milfoils. But at $3 to $5 apiece, the little bugs are expensive.

Herbicides can be used, but the chemicals also affect native plant life and can carry risk for people and fish as well. Because of that, Maine considers chemicals a last-resort treatment. Still, both Fairlee and Lake Morey in Vermont have turned to herbicides when divers and other methods have failed to contain milfoil.

Sometimes, the best you can do is to keep whacking away at the weeds with a mechanical harvester in an annual effort to keep them in check. That’s the case with the water chestnut infestation that plagues Lake Champlain.

All of which emphasizes why prevention is so important, and on the scale of things, painless. Most invaders are unwittingly carried from lake to lake on boats, trailers, anchors, fishing tackle, or even duck decoys. Sometimes they come in on the pontoons of a seaplane.

That’s why it’s essential for people to inspect their boats and trailers or planes, as well as other aquatic equipment, and remove the weeds.

Meanwhile, organizations throughout New England are training volunteers to do regular invasive plant patrols on their lakes, the better to detect invaders before they get a grow-hold. The websites of the Maine Volunteer Lake Monitoring Program ( and the Northeast Aquatic Nuisance Species Panel ( are great resources for information and contacts. Lake lovers should take some time to learn the basics. If they see a suspicious plant, they should get a sample and notify the experts so they can take a closer look. That way, they can help ensure that their favorite body of water doesn’t get left in the weeds.

Scot Lehigh can be reached at