A lakewide algae bloom began about two weeks ago on North Pond, seen at left in this aerial photo. Little North Pond, at right, has been largely unaffected by the bloom. Photo courtesy of Alexander Wall, 7 Lakes Alliance board member

SMITHFIELD — An algae bloom on North Pond has improved in recent days but could worsen with the withering heat that has moved into central Maine, according to a scientist with the 7 Lakes Alliance conservation group.

The algae on North Pond began blooming about two weeks ago during a patch of hot weather, making the pond resemble a bowl of pea soup, according to Danielle Wain, lake science director for 7 Lakes Alliance, which works to preserve land and water in the Belgrade Lakes region.

A recent measurement yielded a water clarity of 4 feet and the organization recommends avoiding prolonged contact with green water. People are urged not to go into the water if the clarity drops to 3 feet, which is consistent with guidelines established by the state Department of Environmental Protection.

“If you can’t see your feet in the water then you probably shouldn’t spend a lot of time in the water,” Wain said Thursday.

She explained that North Pond has about twice as much phosphorus in it than other Belgrade lakes, and it is not entirely clear why. One factor is the pond is a comparatively large watershed with lots of streams and tributaries leading to it that carry in phosphorus following rainstorms.

Phosphorus is an essential nutrient for plant life but when there is too much of it in water it can speed up something called eutrophication, which causes a dense growth of plant life and depletes oxygen levels. A bloom subsides once the algae consumes the available phosphorus.

Wain said North Pond has had greenish waters over the years but the problem has worsened since an algae bloom occurred in 2018. Similar blooms have occurred each year since, she said. The one occurring now has stretched across the length of the pond, which is nestled between the towns of Rome and Smithfield.

“We’re trying to find out where the phosphorus is coming from so we can manage it,” Wain said.

Warmer temperatures spur algae growth and the region is contending with several days of hot, sticky weather. Temperatures are expected to top out in the mid 90s on Sunday before they moderate next week, according to the National Weather Service.

She noted that nearby East Pond used to see algae blooms each year but remediation efforts have improved the condition of that lake.

“We’re very fortunate that none of our other lakes have had blooms like this in recent history,” she said.

Little North Pond, or Little Pond, is connected to North Pond but has not experienced the bloom to this point, which may be because minimal water is exchanged between the two bodies. Other factors may be the absence of development around Little North Pond and differences in sediment and depth, the 7 Lakes Alliance said in an earlier news release.

Wain said “there’s a big team of people working on this in an effort to alleviate the problem” on North Pond, and added that the North Pond Association received a grant from the state to develop a watershed management plan. The association will work with 7 Lakes and others on that plan.

The alliance noted in the earlier release that development along the pond — with homes, camps and gravel roads close to the water — is contributing to the algae blooms, as it allows phosphorus to more easily flow into the water.

The president and chief executive of 7 Lakes, Laura Rose Day, said in the release that algae blooms and the threat of blooms are an ongoing concern throughout the Belgrade Lakes watershed.

“That is why we and our partners must remain vigilant on efforts to minimize erosion, conserve land and educate people on how they can be part of the solutions,” she said.