Boaters enjoy Androscoggin Lake on a sunny, warm Thursday. Officials are warning that an algae bloom has formed at the lake, and the nonprofit 30 Mile River Watershed Association is recommending people stay away from areas of the lake with visible algae or where water is discolored or has an odor. Joe Phelan/Kennebec Journal

For the first time since last September, a lakewide algae bloom has formed at Androscoggin Lake, according to officials.

The algae bloom has led the nonprofit 30 Mile River Watershed Association to recommend people stay away from areas of the lake with visible algae or where water is discolored or has an odor. The 4,000-acre lake spans areas of Wayne in Kennebec County and Leeds in Androscoggin County.

The primary cause of the bloom, a cyanobacteria called Dolichospermum, is capable of producing toxins harmful to humans and animals under certain conditions, which can change suddenly and are difficult to observe.

The 30 Mile River Watershed Association and the Maine Department of Environmental Protection recommend staying away from areas with scum, a paintlike algae collection that usually forms near shorelines. Scum areas have the highest levels of potential toxins and are especially harmful if swallowed.

In open, nondiscolored water, recreational activities should be safe, according to Linda Bacon, a lake biologist with the Maine DEP.

Since the event at Androscoggin Lake meets the state’s criteria for a lakewide algae bloom, the guidelines for staying away from any areas with algae should be applied to the entire lake, according to Lidie Robbins, executive director of the 30 Mile River Watershed Association.

The nonprofit group especially recommends keeping children, pets and livestock away from the lake because they are particularly vulnerable to swallowing the potentially harmful algae.

“When in doubt, stay out (of the lake),” Robbins said.

Boats in August 2020 at the Androscoggin Yacht Club on Androscoggin Lake in Wayne. Officials are warning that an algae bloom has formed at the lake, and the nonprofit 30 Mile River Watershed Association is recommending people stay away from areas of the lake with visible algae or where water is discolored or has an odor. Russ Dillingham/Sun Journal file

Officials said the association discovered the algae bloom during testing Monday morning, when it found water clarity levels had dropped over the weekend to 1.79 meters, a 0.3-meter decrease and less than the 2-meter threshold the state considers a lakewide “nuisance” bloom. The state considers a water clarity level of less than 1 meter a “harmful” algae bloom.

The algae bloom at Androscoggin Lake is happening earlier than in previous years, Robbins said, because of the levels of heat the area has experienced this summer. Lake surface temperatures reached about 81 degrees in early July, the warmest the group has measured since August 2016.

Warm water causes a longer growing season for algae and promotes its growth, causing longer and more potent algae blooms, Robbins said.

Last year, an algae bloom did not form at Androscoggin Lake until Sept. 7, and was above the threshold just two weeks later. Because algae blooms generally subside when temperatures cool, Robbins said this year’s bloom could last much longer than in previous years.