There’s a mystery in Highland Lake.

Every July for the last four summers, a bloom of blue-green algae has appeared in the lake on the Windham-Falmouth town line. The little particles that make up the bloom are called picocyanobacteria, and they disperse in the water in a different way than they do in other lakes. There is no evidence that this bloom is toxic, but it causes a pervasive and noticeable cloudiness in the water.

No one knows for sure why this bloom happens like clockwork every summer. The phenomenon has not been observed in any other lake in Maine, at least so far.

“It seems like this lake is the first time we’ve seen it take over, basically,” said Jeff Dennis, a biologist with the Maine Department of Environmental Protection. “I really want to understand what’s going on here – not just for Highland Lake, but so we know whether this is something that may be coming for other lakes.”

That quest is making waves in Windham and Falmouth.

The Highland Lake Association successfully lobbied the Windham Town Council to pass a moratorium on construction near the 623-acre lake, based on the lake association’s concerns that runoff from developments is contributing to the blooms. The lake association also is circulating a petition to permanently block high-density development in the watershed, an 8.5-square-mile area that drains into the lake. As a result, projects ranging from subdivisions to single homes and garage add-ons have come to a standstill, and the developer of a major project in Windham is threatening legal action.

“In my opinion, it was a quick witch hunt to stop my project,” said John Chase, owner of Chase Custom Homes, who wants to build 34 single-family homes and rental units in the watershed.

Meanwhile, the towns of Windham and Falmouth have pledged to review their zoning ordinances and plan for the lake’s future. The lake association also convened a private roundtable of 15 scientists and officials last week to trade hypotheses on the mysterious bloom.

“This lake is in trouble,” said Rosie Hartzler, a Windham resident and the president of the Highland Lake Association. “If our mission is to preserve and protect the lake, we have to step up.”

A popular spot for fishing and boating, Highland Lake is only 7 miles from downtown Portland.

Local assessors estimated that 250 homes have frontage on the shoreline, and more than 1,000 are located in the 8.5-square-mile watershed. The lake is split by the town line that separates Windham and Falmouth, though its dam is located in Westbrook. The waters empty into Mill Brook, which flows to the Presumpscot River.

PHOSPHORUS OFTEN BREEDS ALGAE

Development within a watershed is a well-documented risk factor.

Phosphorus, one of the major nutrients needed for plant growth, is naturally found in Maine soils, and it’s also in commercial lawn fertilizers. When soils or fertilizers get washed into the lake by storm runoff, the phosphorus effectively fertilizes the lake and can cause algae to multiply into a visible bloom.

Development can lead to more phosphorus loading in a lake by causing sediment erosion, introducing new lawns and fertilizers into a watershed and by producing more stormwater runoff from rooftops, roads and driveways.

In the 1990s, Highland Lake was so murky that it landed on the state and federal list of “impaired lakes.” The lake also had seen a decline in dissolved oxygen needed to support fish. With nearly $1 million in grants, the help of the Cumberland County Soil and Water Conservation District, and the efforts of local residents, it was removed from that list in 2010.

But in late July 2014, the strange bloom appeared for the first time.

“The lake looks pretty green and very cloudy,” said Dennis, the DEP biologist. “It’s a bloom that comes and goes really quickly, but does definitely affect the apparent water quality very dramatically to people who are sitting in a boat.”

Dennis, who works in the Watershed Management Unit at the Maine DEP, said picocyanobacteria is a type of algae often present in lakes, but it is usually not so dominant, and it does not usually behave like the bloom in Highland Lake. This picocyanobacteria is very small and dispersed throughout the lake, while algae in other blooms observed in Maine tend to be larger and cluster in groups. While some algae can be toxic, Dennis said there is no evidence yet that this bloom is harmful to humans, fish or other animals.

Still, nearby residents said the bloom makes the lake uninviting.

“If you’re in the water up to your waist, you can’t see your feet,” said Dennis Brown, who lives on the lake in Windham and acts as treasurer of the Highland Lake Association.

Earlier this year, the town of Windham gave a $4,000 grant to the Highland Lake Association to study the recurring bloom. The association also used $2,000 from its general fund for that research.

Last Friday, the 15 participants at the roundtable came from town and state offices, the Cumberland County Soil and Water Conservation District, the Casco Bay Estuary Partnership in Portland and the Bigelow Laboratory for Ocean Sciences in East Boothbay. Dr. Karen Wilson, an associate research professor in the Department of Environmental Science and Policy at the University of Southern Maine, moderated.

Before the roundtable, Wilson said the group would talk about possible causes for the bloom, what data to collect to test those theories, and funding sources for that work. In addition to development in the watershed and increasing levels of phosphorus, Wilson said she also wants to know whether the resurgent alewife population has contributed to the bloom in some way. The notes from that discussion were not yet available Friday.

TOWN PASSES CONSTRUCTION MORATORIUM

One big unanswered question is whether what’s happening in Highland Lake could happen in other water bodies in Maine, a state that is rich with lakes and valuable lakefronts.

“Economically, it’s a huge deal,” Wilson said. “Maintaining good water quality in our lakes reaches beyond the homeowner who owns some land on the lake. It reaches out into the fabric of the economy in various parts of the state.”

One of the documented trends is the increasing amount of phosphorus in the lake, which is likely associated with nearby construction. “For a lake watershed in Maine, it’s a very high growth area,” the DEP’s Dennis said.

Usually it takes more phosphorus in a lake to see the kind of blooms Highland Lake is experiencing, the biologist said, and scientists can’t be sure yet that phosphorus is the cause of this one. But he said he generally supports any measures to reduce runoff into a lake.

“I’m a strong advocate for minimizing the phosphorus that goes into lakes and keeping them as natural as possible,” Dennis said. “Whether it will get rid of the (bloom) will depend on the cause of the bloom. That’s something we will need to sort out, but I would applaud any efforts that are going to result in less phosphorus in the lake.”

Windham and Falmouth are among the fastest growing towns in the state.

Housing starts in greater Portland have surged, but the supply is still not enough to meet the demand. A shortage of homes for sale in southern Maine has created a frenzied real estate market.

In January, the Windham Planning Board took up a preliminary plan for a new subdivision by Chase Custom Homes. The proposal calls for 10 rental townhouses and 10 storage units, as well as a gated community with 24 single-family homes.

In May, another developer submitted plans for a cluster subdivision with 17 homes to be called Babbidge Farms.

Both developments fall inside the Highland Lake watershed.

Then, in September, at the urging of the Highland Lake Association, the Windham Town Council unanimously passed an emergency 180-day moratorium on construction in the watershed. That measure imposed a sweeping ban on clearing, earth moving and vegetation removal, as well as construction of driveways, parking spaces and patio surfaces larger than 500 square feet.

“The council is concerned that current development, as well as any potential new development, would contribute more nutrients to the lake and potentially cause irreparable harm to the lake,” Windham Town Manager Tony Plante said.

DEVELOPER CONSIDERS LEGAL ACTION

State law already requires shoreland zoning to protect water bodies in Maine, but the town is using the pause in development to strengthen its ordinances to better prevent runoff into the lake. Proposals include requiring additional erosion control at development sites and adopting a point-based permitting system that encourages homeowners to add runoff protections to their properties.

In total, according to town records, the moratorium temporarily blocked the construction of the two subdivisions, nine individual homes, three garages, an accessory apartment, a deck and a basketball court.

The developer of the Babbidge Farms project withdrew the application in October.

Chase Custom Homes development has since received its required permit from the Maine DEP. But the moratorium put a hold on the project, and the state permit has been appealed by the Highland Lake Association. Chase said he has invested $1.3 million into the subdivision, and he has buyers ready to pay $400,000 to $700,000 for the single-family homes.

While he waits, Chase said he is considering legal action, though he would not elaborate more on whom he would target with a lawsuit. He argued that the local and state permitting process he has gone through already requires him to include protections against runoff in his plans, which would be an improvement on the existing property. He said those new erosion barriers would help, not hurt, the lake.

“All of these problems are from prior lack of homeowner responsibility to protect that lake,” he added. “It’s their doing, not mine.”

Other critics of the moratorium included Jim Lydon, who had planned to build his first home in Windham with his partner. They needed to leave their apartment by January, but the moratorium has stalled their construction.

“We’re asking that you please, very seriously, consider the impacts this will have on us and many other people who are in our situation as well,” Lydon told the Windham council in October.

While there has been less development pressure in Falmouth, Town Manager Nathan Poore said the council there also will review its ordinances to better protect the lake. He said the possibility of a moratorium has come up in conversation, but it has not been formally considered by the council.

The Highland Lake Association wants to go even further to restrict development. The board is circulating a petition to permanently block high-density development in the watershed. Hartzler, the Highland Lake Association president, said they have collected 500 signatures so far; they need at least 1,200 from registered Windham voters to prompt a public hearing.

Meanwhile, officials from Windham, Falmouth and the Highland Lake Association have agreed to form the Highland Lake Leadership Team to help monitor the water quality and compare ordinances.

“There are known ways of improving water quality in the lake,” Poore said. “We don’t have to learn more about the mystery specifically to make progress on those best management practices.”

Megan Doyle can be contacted at 791-6327 or at:

mdoyle@pressherald.com

Twitter: megan_e_doyle

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CORRECTION: This story was updated at 3:30 p.m. on Dec. 9, 2017, to correct the hometown of Rosie Hartzler, who lives in Windham.