For years it seemed nothing would stop the spread of Eurasian watermilfoil in Candlewood Lake, but 2017 might be a turning point.

Some coves on Candlewood and neighboring Squantz Pond had virtually no milfoil this year — a stark contrast to previous years, when the invasive weed fouled boat propellers and tangled the limbs of unwary swimmers.

“In portions of the lake, it was a complete 180,” said Larry Marsicano, former executive director of the Candlewood Lake Authority, now a consultant.

The news was not so good in nearby Lake Lillinonah. Greg Bugbee, who oversees the Invasive Aquatic Plant Program for the Connecticut Agricultural Experiment Station, said milfoil infestation on that lake is “the worst I’ve seen it.”

Bugbee noted these stark differences while mapping the plants this summer on all three bodies of water.

On a scale of 1 to 5, Bugbee placed the acreage and abundance of milfoil at Candlewood and Squantz this season at 2.5, far below last year’s rating of 4.5.

“The milfoil was nowhere near the proliferation and nuisance it was last year,” Bugbee said. “I wasn’t getting complaints about weeds this year like I normally do. Fishermen seemed to be happy.”

Bugbee suspects the improvement is owing largely to the thousands of sterile grass carp released in Candlewood over the past few years and Squantz this summer to feed on the milfoil.

He said he saw schools of grass carp in several coves while monitoring the lake, including Shelter Cove, Allens Cove, Brookfield Bay and to some extent Lattins Cove. He saw coontail, a native aquatic plant the carp avoid, covering the lakebed in the coves.

“This would tell us there’s a decent chance the grass carp are preferring the coves and feeding there,” he said.

Theodora Pinou, a Western Connecticut State University professor who led the study tracking the carp at Candlewood, said she saw schools of carp in the coves.

Forty-eight carp are fitted with tracking devices. Luke Mueller, one of two interns who assisted Pinou tracking them this summer, said they spotted four of the tracker-bearing fish in Shelter Cove.

Marsicano suspects a change in the winter drawdown of lakewater levels could have helped. Last year, FirstLight lowered the water earlier than it has in about 15 years, letting the plants dry out and exposing them to deadly cold before they could be insulated by ice or snow.

At Lake Lillinonah, by contrast, milfoil infestation was far worse in 2017 than in previous years.

For every acre of milfoil-infested water two years ago, Bugbee said, there were 10 acres this summer.

Greg Petriccione, chairman of the Lillinonah Lake Authority, said he suspects zebra mussels, an invasive species that might have contributed to the spread of the milfoil this year.

Zebra mussels feed on organisms strained from the water, leaving the water clearer and letting sunlight in to penetrate and help the milfoil grow, Petriccione said.

Homeowners have been cutting the milfoil without collecting the pieces, which can take root and grow, he said.

Petriccione said the authority is working with its advocacy group, Friends of the Lake, to create a milfoil management plan.

Len Greene, a spokesman for FirstLight Power Resources, which oversees area lakes, including Lillinonah, said the company lacks the authority to create management plans or choose treatmentsfor water-quality problems.

“We are however very supportive of the community’s efforts to eliminate the milfoil and we’ve funded several projects over the past year,” he said.

In the meantime, Petriccione said, homeowners can manage the milfoil independently, removing it by hand or machine or using benthic barriers — films or fabrics that keep plants from taking root in the lakebed.

kkoerting@newstimes.com; 203-731-3345