Thirty tons of algae and muck came out of Lake Mamanasco

Sucking green gunk with a floating suction harvester, scooping out glop by hand, pulling out sticks, branches, tree trunks, even a dock, crews from Aquacleaner Connecticut have removed an estimated 30 tons of algae and organic debris from the north end of Lake Mamanasco.

We will have removed at least 30 tons of filamentous algae in approximately five weeks of work ending on Friday,” Mark Amler, a partner in Aquacleaner Connecticut, said Tuesday.

Much of what was removed was in a thick algae mat that covered much of the north end of the lake.

“I threw a shovel on there, and it doesn’t move,” Amler said.

“We had maple saplings growing out of the mat. And grass.”

The job, expected to be finished up Friday, has for the last five weeks employed a crew that ranged from three to six men. They’ve been out there in diving suits with their suction harvester, and an old boat they use as a refuse barge, cleaning the lake.

“There is a huge difference in the before and after,” said Barbara Hartman of the Mamanasco Lake Improvement Fund, the neighborhood association that hired Aquacleaner.

“The progress is easily seen — clear water now, versus algae mats four to 12 inches thick, extending 100 feet from shore before,” she said.

It has already made the north end of the lake more useful for recreation — one of the $40,000 project’s goals.

“You can get boats in the area now, while that was impossible before,” said Hartman. “Fishermen are already fishing in the area; this was impossible before.

“We have reclaimed large areas of the lake that were turning into marsh with bushes growing on the mats.”

Still, it remains unlikely the north end of Mamanasco will have much attraction for swimmers.

“The water is fairly shallow here, and the bottom is very ‘mushy’ so I doubt there will be much swimming in this area,” Hartman said.

Water pump

The approach is simple.

“We suck it out with what’s called a suction harvester, which is essentially  a water pump, a heavy duty water pump, attached to an engine,” Amler said.

Workers in diving suits uproot plants that are attached to the bottom and feed them into the suction hose.

The water flows back into the lake, and bio-mass is retained in bags.

“It deposits the algae mat we take out, and the sticks and leaves and whatever else, into onion bags,” Amler said. “Fifty-pound onion bags, like you’d buy in grocery store.”

The bagged muck is dried out, and trucked away.

“And that’s pretty much the project,” Amler said.

There have been a few surprises on the lake bottom.

“We found a dock in the lake,” Amler said.

It was out about 20 feet from shore.

“It had to be in there a long time,” Amler said.

Amler’s estimate of 30 tons of gunk removed from the lake is based on truckloads carted off.

“Weight or mass is calculated by the cubic volume of material removed by truck,” he said. “One cubic yard is equal to one ton of weight. Three cubic yards per truck haul, eight trips so far, equals 24 or so tons,” he said Tuesday. “Another five to ten yards coming.”

The algae mat

Much of the material came from the algae mat — which was a substantial thing, a kind of eco-system, an organic being in a way.

“That mat’s a different animal. It’s solid,” Amler said. “Like I said, you could throw a shovel on it and it doesn’t even move.”

Still, 30 tons of gunk?

“The way we end up with that kind of tonnage, that mat has varied in depth or density anywhere from three inches to six or seven inches,” Amler said. “It basically took like a U shape, so we went up the shoreline at least a couple of hundred feet on the side closest to the high school, and on the other side just around the bend in the road, where Mamanasco Road bends around, and from the shoreline out I’d say — this varies based on where the mat was — anywhere in width from say 100 feet to 65 or 70 feet out, at its thinnest.”

Lake Mamanasco may be slowly evolving toward becoming a swamp, as many lakes do. Amler says the problem was likely moved along by years of chemical treatments to kill weeds.

“When you do chemical applications you kill the plants but it’s not removed. It goes down to the bottom,” he said.

In Mamanasco, the north or northwest end is most plagued by algae and plants.

“The prevailing wind tends to sweep everything to the end of the lake,” Amler said.

“Everything kind of floats down to that end and it just becomes this giant mat of interwoven, thickening thatched organic debris,” he said.

That’s why the Mamanasco Lake Improvement Fund chose to have the northwest end suctioned out with its $40,000 investment.

Richardson Grant

The project was financed with a $30,000 grant from the Anne S. Richardson Fund — the late Ms. Richardson’s home, now Richardson Park, overlooks Mamanasco from above the cliffs — and members of the Mamanasco Lake Improvement Fund or MLIF added $10,000. No Town of Ridgefield money went into the project.

The project actually started late last fall, but most of what got done was accomplished this spring, according to Amler.

“We probably spent three and a half weeks there in the fall, but they weren’t fully productive weeks,” he said.

“A lot of that had to do with weather and environmental conditions  changing,” he said.

“The middle of November, the fall, we actually had ice on the lake. It got very cold very early. And then it actually warmed up in December,” he said.

“From my perspective it was kind of a lesson learned,” he said.

“Don’t start late in the fall.”

Hartman said the lake area residents like what they’re seeing — although people wonder how long the north end’s cleanup will last.

“We are very happy with the results. Aquacleaner has done everything they contracted for and more. As far as I am concerned, this is the best use of any money we have ever spent, assuming it stays algae clear,” Hartman said.

“If the results hold up, I would hope to apply for more grant money to work on other areas of the lake,” she added. “We started with the northwest corner because it was the worst by far. But the opposite end of the lake would certainly benefit from a similar project, as well as some of the coves in between.”

Amler said the suctioning out algae and organic sediment should improve the water immediately, and slow the process that’s mucking up the lake — but he isn’t promising there will be no more algae.

“In terms of what it does for the lake, for one thing that organic sediment is rich in nutrients which ultimately feed additional future algae blooms. So, by doing what we’re doing, we’re hoping to preserve whatever depth exists in that end of the lake, which at the same time eliminates or limits the food course for additional algae growth.

“Does that mean they’re not going to have additional algal growth? No. That means we’ve eliminated something that’s built up over time…

“I’ve lived in Ridgefield four and a half years, and I’m very familiar with Mamanasco Lake, and I can tell you that end of the lake hasn’t seen moving water during the spring or summer since I’ve lived here,” Amler said.

“Right now, it looks great. Is more algae going to accumulate there and grow there? Yes. But it won’t get like it did for some time.”

Lake association members are eager to have the results last.

“We hope, but can’t be sure, that this end of the lake will remain algae free,” Hartman said. “But with winds blowing algae and weeds to this end of the lake all the time, only time will tell.”

 

Photo: Nick Coon of Aquacleaner Connecticut scooped muck out of the northwest end of Lake Mamanasco, where the company was finishing up five weeks of lake cleaning. Behind him at center is a boat used as a “refuse barge,” and at right is the “suction harvester” that cleans the lake bottom. —Macklin Reid photo

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