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GROTON — If an invasion of non-native plant species continues to spread unabated, Lost Lake will soon live up to its name and really be lost not only to the concerned owners of lake-area properties but to the entire town.

Although the issue of invasive plant species such as milfoil, combomba, water chestnut, and clouds of free floating filamentous has been around for many years, only recently has the problem reached crisis proportions with forests of plants carpeting the bottom of the lake.

Seen from above water, the various plants can be spotted mostly along the shorelines where their flower stalks and tough, ropy tendrils break up the lake’s placid surface. Farther out, clear surfaces are deceiving and where sunlight penetrates beneath the water, coils of combomba and milfoil can be seen, their sometimes 6- and 7-foot long tendrils, thick as heavy wire and as tough as cables, wave enticingly like a Brazilian rain forest as seen from an airplane.

Indeed, in places where the weeds grow thickly, parents have been known to warn children from swimming in them for fear they might become entangled in the strands and drown.

“When I was a kid, my friends and I explored every nook and cranny of Lost Lake and Knops Pond,” said Art Prest, whose Weymisset Road home overlooks Knops Pond. “We would take canoes up Martins Pond Brook (a major feed to Lost Lake), which was pristine back then. Now you can’t get to it by kayak or canoe because of a downed tree, but the last time I went up before that tree fell it was in terrible condition with all kinds of green growth in the water. It was full of trout many years ago but there were no trout when I visited it some years ago.

“When I was younger we had native weeds growing on the bottom and lily pads on the surface,” continued Prest, who summered on the lakes when he was a child in the 1940s. “In the last 30 years, the lakes have become choked with nonnative invasive weeds that are choking out the native aquatic plants and taking over the entire lake bottom and surface. Underneath the native lily pads is a sea of invasive weeds. In the 1990s a letter was sent to the selectmen saying that 15 percent of the lake was suffering from the growth of non-native invasive weeds and asked for help. In 2011 the Groton Lakes Association commissioned Aquatic Control Technologies to do a survey of Lost Lake and Knops Pond and then reported that almost 60 percent of the lakes were infested with these invasive weeds, including a few plants of water chestnut, a weed that could totally destroy these two lakes in less than three years if nothing is done. In short, our lakes are dying and will turn into a swamp if we don’t take action.”

Prest, a member of the Great Ponds Advisory Committee and president of the Groton Lakes Association, said it would be in the town’s interest to help restore the lakes because if they continue to deteriorate, shoreline property values will fall along with taxes that could be collected on them.

In a recent boat tour of the lakes, the invasive species could be seen everywhere with obvious channels cut through the heaviest growth by a weed-harvesting machine whose mechanical approach to the problem barely suffices to keep swimming areas open.

“Over the last 25 years, we have tried multiple approaches to deal with the problem but the only solution that worked was the use of herbicides in 2002 to 2004,” said Prest, sitting at the wheel of his motor launch and pointing out whole stretches of lakefront taken over by the invasive weeds. “We currently use a harvester that was purchased by the Groton Lakes Association and donated to the town. The harvester keeps paths open for recreation but can’t possibly keep up with the expansion of the coverage of the invasive weeds. The harvester mows the “lawn” but the “lawn” coverage keeps expanding faster than we can mow it.”

Gerrett Durling, chairman of the Weed Harvester Committee, agreed, pulling up strands of combomba from the side of the boat to demonstrate the toughness of their tendrils which can pose a hazard to swimmers.

“I’ve seen people come out of the water with red marks circling their arms from where the plants wrap around them,” said Durling.

Adding to the problem, said Alex Woodle, also a member of the Great Ponds Advisory Committee and longtime lakes area resident, was last year’s mild winter, which to a great degree prevented ice from forming on the lakes. Ice inhibits weed growth during the colder months. With the warmer temperatures, he said, weed growth merely picked up where it left off last fall.

Another piece of the puzzle is the issue of septic disposal at Lost Lake, where most lots are too small to allow wastewater systems complex enough to satisfy the letter of the state’s Title 5 law. Currently, plans are in the works to install a new sewer system in the neighborhood connected to treatment facilities in Ayer.

“We need to work toward safely eradicating the non-native invasive weeds while protecting any endangered aquatic plants that might exist,” said Prest of how to approach the problem. “Eradicating the invasive weeds is the number-one priority, but a Lost Lake sewer project is critical to decreasing the nutrients that have been feeding the growth of these weeds.”

Complicating efforts by various groups concerned about the health of the lakes, including the Great Ponds Advisory Committee and the Groton Lakes Association, has been the need to work with and through local and state regulators dealing with open-water issues.

Continued next week.