The extent and density of a nuisance weed infestation at Taunton Lake has been significantly reduced, based on the results of an August 23 survey of the lake’s shallow-water perimeter, which is the habitat of the pesky invasive aquatic plant commonly known as water milfoil.

The reduction of milfoil is thought to be the result, at least in part, of past stockings of the lake with grass carp, a fish that eats milfoil.

Milfoil infestation of water bodies is a common problem in North America in lakes and waterways. Many lakes in the area have milfoil infestations, including Lake Zoar and Lake Lillinonah, both of which are impoundments on the Housatonic River. Candlewood Lake also is infested. The plant is native to Eurasia.

Milfoil infestations make water conditions irksome for swimmers, anglers, and boaters because the weeds tend to get tangled up on swimmers’ limbs, on fishing tackle, and on boat oars and propeller blades. It has long stems from which long needlelike leaflets radiate. Milfoil is transferred among lakes when fragments of the invasive weed cling to boats that are then placed in other lakes.

George Benson, the town’s planning director, is a limnologist by training. Limnology is the study of lakes and other bodies of fresh water. Since milfoil was discovered in the lake in 2007, Mr Benson has advised the private Newtown Fish & Game Club and the private Taunton Lake Landowners Association on measures that could be taken to curb the weed’s spread.

Mr Benson said this week there has been “a significant reduction in the area of [milfoil] weeds, and the density of weeds” in the lake. “It’s a huge improvement,” he said.

About four acres of milfoil infestation in Taunton Lake was first noted in 2007 in the shallow waters at the southeastern end of the 126-acre spring-fed, glacial lake, near an old brick pump house. Milfoil was later discovered in the shallow-water southwestern section of the lake near a dam and at the Newtown Fish & Game Club’s boat launch at the northwestern end of the lake.

Milfoil requires sufficient sunlight to grow in shallow water, where water clarity also promotes the plant’s growth. In Taunton Lake, the deepest water in which milfoil is found is five to six feet deep, Mr Benson said. The lake’s deepest point is 29.5 feet.

On August 23, Mr Benson; Steve Maguire, the town’s senior land use enforcement officer; and Kevin Dunkin, the town’s Geographic Information System (GIS) specialist methodically toured the lake’s perimeter in a 12-foot johnboat. Mr Dunkin plotted the presence of the nuisance weeds to gather data for a map that will depict the weed’s current extent and density in the lake.

At its worst degree of infestation, milfoil was present in about 18 acres of the lake, along its perimeter. The area where milfoil remains is much smaller than in the past, and the milfoil growth there is relatively sparse, according to Mr Benson. He noted that the milfoil no longer floats upon the lake’s surface.

“Milfoil is pretty hardy,” Mr Benson said, noting that it will grow in the wintertime, provided that sunlight can penetrate transparent surface ice at the shallow areas of a lake.

Mr Benson estimated that the lake now holds about 75 to 80 percent less milfoil than it did in the past. “It’s a nasty weed,” he remarked.

The presence of sterile grass carp, which were placed in the lake in past stockings, likely is responsible to some degree for the milfoil’s decline, he said. In past stockings, the lake received several hundred grass carp to create a population of fish that would consume the milfoil as food. Grass carp that were about one-foot-long when stocked can grow to more than three feet in length.

It is thought that some smaller grass carp, which were placed in the lake in an initial stocking, may have been the prey of largemouth bass. Later stockings employed larger carp.

As a private limnologist, Mr Benson has overseen a successful milfoil control project at the 83-acre Ball Pond in New Fairfield, where grass carp were placed in the water and have been eating milfoil for years, thus controlling the weed.

Anglers who catch a grass carp at Taunton Lake are asked to put the fish back in the water to let it continue eating milfoil.

Taunton Lake is ringed by private properties and has only limited public access. Only the southern side of the lake has dense residential development, with other lake sections being either lightly developed or undeveloped.