Lake Mamanasco: Management means care, chemicals, science, money


Lake Mamanasco is recovering from its bout with blue-green algae in 2015, and moving toward a more favorable ecological balance under the care of the loosely allied homeowners of the Mamanasco Lake Improvement Fund.

“This is a lake, it’s not a swimming pool,” said Barbara Hartman, president of the Mamanasco Lake Improvement Fund. “It’s never going to be clear like a swimming pool. We want it to be usable, that’s our goal.”

With a roughly 89-acre surface area, Mamanasco is the largest lake in town. Relatively shallow — the maximum depth is eight feet and the average depth six feet — the lake contains 534 acre-feet of water.

The uses of Mamanasco’s waters are largely swimming, fishing and boating. It’s not a direct drinking water source, although it does drain into the Titicus River, which is eventually a tributary to the Titicus Reservoir in North Salem, one of 12 reservoirs in New York City’s Croton watershed.

Mamanasco is currently being monitored and treated by The Pond and Lake Connection, a Brookfield-based firm hired by the improvement fund last year.

“This is our second year on that lake,” said Jeff Stahl, head of The Pond and Lake Connection.

“We were brought in because in 2015 the lake was closed because of blue-green algae, which is a toxic algae — it’s harmful to animals and humans if ingested.”

The company is also involved in managing Lake Pierrepont, Rainbow Lake and the small pond in front of the Fox Hill condominiums.

Fawn Young, an aquatic biologist with The Pond and Lake Connection, oversees Mamanasco’s management.

“When we came on board it was in a very, very bad state,” she said. “It had these potentially toxic blue-green algae blooms. Blue-green algae is not even really an algae, it’s a bacteria that can photosynthesize. They are capable of producing toxins that can be fatal to, primarily, animals — if a dog drinks the water. It can make people sick, give them skin rashes.

“In 2015, the lake was closed due to these toxic blooms. After that is when the board asked us to come on and manage this lake,” Young said. “Our primary goal is to try to reduce the chances of a toxic bloom.”


To battle the blue-green algae and also invasive plant species such as curly-leaf pondweed, the lake gets chemical treatments, mostly with the algicides.

Paperwork for the treatments lists six different chemical products — Cutrine Plus, Cutrine Ultra, SeClear, Sonar, Clipper, Reward — and what’s used during a particular treatment will vary.

“I will not use all of those,” said Stahl. “The list of products there just gives me some flexibility, depending on the species of algae I’m seeing, and or weeds.”

All treatment chemicals used must be approved by the state.

“Connecticut state law requires us to list which chemicals we’ll potentially use during a treatment,” said Young. “I use a variety of algicides. They’re all chemically formulated to target just aglae — they don’t hurt the plants...

“We do target one plant in there. There’s an invasive, curly-leaf pondweed, it actually outcompetes the native plants. It’s not good habitat for wildlife and nothing uses it for food, so it doesn’t have any predators, so it outcompetes the rest of the plants in the lake, which is bad — then you’d have a mono-culture.

“We actually treat that in April before any of the native plants come up. We’re trying to eradicate that plant, and we can do that because of its growing cycle and timing the treatments. We kill that before any of the natives come up, and leaves the natives unharmed.”

Half and half

A crew from the Pond and Lake Connection can periodically be seen on Mamanasco, going around in their fan boat, doing chemical treatments.

“We’re only allowed to treat, at most, half the lake at one time,” Stahl said. For the 89-acre lake, that’s about 44 acres.

“That 44 acres is split in half, for each application,” he said. “...We do 20 acres, wait 14 days, and then do another 20 acres.”

The lake will be treated periodically over the course of the season.

The homeowners group is involved.

“Sometimes they tell us, sometimes we tell them the lake is looking bad and it needs a treatment and then we schedule one,” said Hartman.

“They’re deliberately leaving some of the weeds growing in the middle to try to use up some of the nutrients,” she said.

There’s a whole list of things that shouldn’t be done in the lake or with its water for 24 hours after a chemical application: no swimming, drinking, fishing, irrigation, livestock watering.

There is public notification of treatments with legal notices, signs, and email blasts to residents.

“As far as protocol, when we do a treatment the local wetlands [office] is given a 48-hour notification that we’re doing a treatment,” Stahl said. “It obviously goes in the newspaper, and they give us a three-day window around that day — that’s for ponds or lakes with more than one owner, or public access.”

That’s the notifications. Permits for the chemical applications are usually obtained off-season.

“When we send in permits to the state, the local wetlands gets a copy of that application, so at that point they can bring up any concerns that they have,” Stahl said.

“Honestly, the hardest part of our work is in the winter when we’re doing all these permits.”

Clear? No

Homeowners around the lake shore tend to judge the lake on its aesthetics.

“They for the most part would love to see the lake look very clear everywhere,” said Hartman. “It’s our understanding from our lake management company that if we kill all the weeds off, we might get another toxic blue-green algae bloom.

“There have been blue-green algae blooms in other lakes,” she said. “As far as we can tell nobody knows what triggers it, except a lot of hot weather and a lot of nutrients in the water.”

Last year the MLIF got a $2,500 grant from the Anne Richardson Foundation to finance a study of Mamanasco by the Connecticut Agricultural Experiment Station, Department of Environmental Sciences.

“We felt it was very important to get somebody to look at the whole lake and give us their perspective,” said Hartman.

“We really wanted to try to get an independent look at the lake and get someone who’s pretty much an expert in the area to give their thoughts on where we were and what we could do.

“The shallow nature and fertile sediment of Mamanasco Lake makes it prime habitat for aquatic vegetation and algae,” says the 2016 state report Mamanasco Lake, Ridgefield Ct., Aquatic Vegetation Survey, Water Chemistry, Aquatic Plant Management Options, by Gregory J. Bugbee and Jennifer M. Fanzutti.

“Eleven plant species occurred in the lake in 2016 with curly-leaf pondweed and minor naiad being invasive. Curly-leaf pondweed is the biggest problem in the spring while algal mats and native species like small pondweed become a nuisance in the summer.

“Long-term control can best be accomplished by dry dredging although this is often not practical unless the sediment and under burden can be sold.”

The findings, delivered in March of 2017, can be found online under Mamanasco Lake Final Report 2016.

“The long and short of it, on what they found: The chemical treatments we were doing were the best way to keep the lake useable,” Hartman said..

“The perfect option — which we can’t afford, because it costs $5 million — is to have the lake dredged, make it deeper,” she said.

The lake’s history includes past chemical treatments, and a number of years when plants were controlled by regular mechanical harvesting — a floating weed harvester regularly patrolled the waters. The mechanical harvesting can have a downside.

“Harvesting or mechanical removal has the benefit of providing immediate control but problems include rapid regrowth, finding suitable disposal sites and spreading of weeds by fragmentation,” says the report by Bugbee and Fanzutti of the state Agricultural Experiment Station. “...Weeds like milfoil … and fawner spread by the rooting of broken pieces. Harvesting practices can distribute the weed throughout a lake. These weeds also have strong root systems that will cause regrowth.”

Past practices help determine how the lake managed.

“In this lake management plan, basically, the lake has been treated aggressively for weeds in the past, so there really was not a lot of native plants growing in there. So our strategy for the blue-green algae is to really get some of the native plants to bounce back in there, come back,” Stahl said.

“That’s why ‘when’ is so important — when you do treat for weeds,” he said.

This spring, Mamanasco was treated early in the season for the invasive curly-leaf pondweed.

“Early in the year, so you don’t have an impact on the native vegetation. You’re treating the curly leaf pondweed before the native plants are even starting,” Stahl said.

“The native plants, they’re mother nature’s best filters and sponges for absorbing the nutrients that are in the lake, so we want native plants and weeds to be there,” said Stahl.

With native plants consuming the nutrients, there’s less in the water to support algae.

“We’re starting to see some of the plants come back, which is great, and we can lessen our rate and frequency with our algae controls,” Stahl said.


Hartman said the Mamanasco Lake Improvement Fund operates largely on donations, though it also seeks grants for projects such as the 2016 study, and has worked with the town on drainage work around the watershed to reduce the amount of nutrients in the runoff entering the lake.

“MLIF isn’t an organization that has dues or anything. What we do is we ask for a contribution from everybody that’s in the watershed,” Hartman said. “There’s 520 homes in the watershed. There are about 60 lakeside homes within that 520.”

About 20% to 25% of property owners in the watershed support the organization financially — the exact number varies from year to year, according to Hartman.

“The percent goes up the closer you get to the water,” she said.

The Town of Ridgefield, which owner substantial Mamanasco shoreline at Richardson Park, budgeted $6,000 for the Mamanasco Lake Improvement Fund in both the 2016-17 and 2017-18 fiscal years. The MLIF was one 19 organizations — from the Ridgefield Symphony to the HART bus service to the Regional Hospice — that share more than $140,000 in community grant money from the town.

MLIF supporters are generally happy with their managed lake, according to Hartman.

“The treatments cost about $30,000 a year. It’s not cheap — very expensive — but it’s very worth it, we feel,” she said.

“The goal is to keep the lake useable for boating and fishing and swimming and other recreational uses.”