FAIRLEE — When Smith Reed and his wife, Ginny, were looking for a lake to live on around 15 years ago, Lake Morey stood out.

“We wanted to find a lake that had clear water,” Reed said. “The water quality has been excellent.”

In recent years, however, that started to change as algae began blooming on the lake each summer with increasing frequency.

“The algae just explodes when it’s very warm out and the lake is calm,” said Reed, who is head of water quality for the Lake Morey Protective Association.

Algae blooms are caused by the release of phosphorus and can cause health problems for people and animals who are exposed to them. They have increased in recent years across the region in part due to climate change and an increase in phosphorus runoff from human activities such as agriculture.

A treatment of Lake Morey this summer seeks to eliminate algae blooms and make the water clear once again.

The treatment involves sending a mixture of aluminum sulfate and sodium aluminate — often referred to in shorthand as “alum” — into the depths of Lake Morey where the phosphorus settles. Workers put the liquid mix into tanks on a barge, which then carries it to designated sections of the lake. People can still use the lake when it is being treated.

The treatment does two things: It removes the phosphorus and “the bigger part of it really is the alum settles down into the sediment in the deeper areas and it can bond with the phosphorus more permanently,” said Dominic Meringolo, senior project manager and environmental engineer at SOLitude Lake Management: Lake & Pond Management Services, which is overseeing the Lake Morey treatment.

The alum is being applied on 379 acres of the 575 acres of Lake Morey where it is 26 feet or deeper, he said. Lake Morey has depths of up to 43 feet and is an average of 28 feet.

The project, which has been in the works for a few years, is being funded by a $816,176 forgivable loan through the Vermont Agency of Natural Resources’ Clean Water Initiative Program, Fairlee Town Administrator Ryan Lockwood said.

“There’s been no negative feedback of this treatment,” he said. “The lake is basically the lifeblood of the town. We want to make sure it’s usable and safe. So much around Fairlee depends on it.”

Reed and other residents have noticed more algae blooms in recent years.

“After a long hot summer, come early September we were seeing blooms of algae we had never seen before,” he said. As the years went on, the algae began showing up earlier and earlier, into mid-to-late July. Reed and his family would avoid swimming in the lake.

“When the algae was blooming, we’d still go boating but we’d have to literally steer our boat around these mats of algae because you don’t want to stir them up,” Reed said. “They’d be as large as maybe 1,000 square feet, 2,000 square feet, the footprint of a house.”

Exposure to cyanobacteria can lead to stomach pain, rash, sore throat and headache, among other health effects, according to the Centers for Disease Control and Prevention.

While not all algae blooms are cyanobacteria, if people observe large algae blooms on water bodies in mid-to-late summer, it’s a good chance they contain cyanobacteria.

“It’s safe to say frequency of blooms is increasing,” said David Neils, chief aquatic biologist in the Water Division of the New Hampshire Department of Environmental Services, who has worked for NH DES for 24 years.

“Yes, we’re seeing more cyanobacteria blooms and they’re occurring more often, but we also have to layer into that that people are much more aware of them,” Neils said.

Heat is a contributor. New Hampshire lakes have an average of two weeks less ice coverage than they used to and open water absorbs more heat from the atmosphere. “This year it was even earlier because we had a much milder winter,” Neils said.

Climate change is a factor in the increasing algae blooms, along with the increase in intense rainfall events in Vermont, Ben Copans, watershed planning supervisor with the Vermont Agency of Natural Resources’ Department of Environmental Conservation, wrote in an email. Such storms cause increases in erosion and nutrient loading which may also be a factor in the higher nutrient levels in some lakes and ponds.

This is the second time Lake Morey has undergone alum treatment. The first was in 1986.

“It was the first lake to have an alum treatment in Vermont,” Copans said in a phone interview. The treatment is also considered safe, and used to treat wastewater and drinking water. “It’s a pretty common way to clean up water in a bunch of different contexts.”

In New Hampshire, there have been three lakes that have been treated with alum, said Neils, at New Hampshire DES. The first was on Kezar Lake in Sutton in the mid-1980s, the second was on Nipple Pond in Barrington in 2021 and the third was this year on Lake Kanasatka in Moultonborough.

Copans, who led a similar alum treatment project on Ticklenaked Pond in Ryegate, Vt., said that, while effective, alum treatment isn’t a solution for all water quality issues in Vermont’s lakes.

“It’s really important that you address the watershed sources,” which can bring phosphorus into lakes, Copans said. It’s important to address where the phosphorus is coming from because if those issues are not addressed — and phosphorus continues to enter the lake after alum treatment is applied — it won’t be as effective.

As part of the research needed before starting the alum treatment, a study was done on the Lake Morey watershed to determine sources of phosphorus. The study found that “people’s lawns and runoff from driveways could be contributing to some levels of phosphorus in the lake,” Copans said. Agriculture was found not to be a significant factor.

“There wasn’t anything that came out of that study that suggested there was a lot of watershed loading to the extent that it would cause a problem with the alum treatment being effective,” Copans said.

The Lake Morey Foundation and Alohoa Foundation joined together to fund a roughly $18,000 grant for a study that included tracking the source of the phosphorus that was needed to start off the planning for the alum treatment, said Bob Wertheimer, president of the Lake Morey Foundation.

“It was something the whole community wanted. In addition to all the subjective reasons we wanted it done for the beauty of the lake and so forth, the lake is a real economic driver to the town and to the Upper Valley,” he said. “We all recognize that and were committed to getting the treatment done as soon as possible.”

Since Lake Morey does not have a lot of inflow from outside water sources — which can bring in more phosphorus — the alum treatment has the potential to last more than 20 years, Meringolo said.

Back on Lake Morey, Reed has already noticed that the water is getting clearer.

“This year I think everybody is going to be very happy with the clarity and the quality of the water,” he said.

Liz Sauchelli can be reached at esauchelli@vnews.com or 603-727-3221.