The bloom was found on Monday at the south end of the lake, where the public beach is located, by a concerned citizen who contacted the Mirror Lake Watershed Association to report it. The discovery was confirmed by the Paul Smith’s College Adirondack Watershed Institute on Tuesday.

“Our volunteers took quick action upon receiving the report,” MLWA President Bill Billerman said in a statement.

A sample of the bloom was delivered to the AWI lab on Monday and analyzed, according to a news release from AWI. The dominant algae was later confirmed to be dolichospermum lemmermannii, a species of cyanobacteria, which could produce cyanotoxins. The state Department of Environmental Conservation’s Harmful Algal Bloom Program has also confirmed AWI’s findings and added it to the state database.

“Cyanobacteria are a natural part of the lake’s biotic community,” Brendan Wiltse, AWI’s water quality director and former science and stewardship director for the Ausable River Association, said in a statement Tuesday. Wiltse has spent years studying Mirror Lake’s water quality.

“The concern arises when dense blooms form,” he added. “These blooms are capable of producing toxins that can be harmful to humans and animals. It is important to note that the presence of a bloom does not necessarily mean that toxins are present.”

If humans or animals touch or swallow water with harmful algal blooms — or inhale airborne droplets — they may experience adverse health effects, according to AWI. According to the state Department of Health, if someone is exposed to high levels of the algae and its toxins, it may cause diarrhea, nausea or vomiting; skin, eye or throat irritation; allergic reactions or breathing issues.

“At this time of year, our primary concern is the safety of dogs and other pets that may enter the lake,” Billerman said. “We encourage the public to avoid letting their dogs enter the water if they are suspicious of whether a bloom is present.”

Those who do come in contact with floating mats, scums or discolored water should rinse themselves — or their pets — off with clean water afterward, according to AWI.

The existence of this harmful algal bloom doesn’t impact the village’s drinking water, which is sourced from Lake Placid, not Mirror Lake, according to Wiltse. The bloom had begun to dissapate Tuesday, Wiltse said, but AWI’s staff and volunteers will continue to check on it.

The cause of this algal bloom is unclear — it’s too early to say for sure, according to AWI — but the possibility of this happening has been talked about by scientists for many years. A report co-authored by Wiltse and Adirondack Watershed Institute researchers Elizabeth Yerger and Corey Laxson showed that road salt and stormwater runoff have contributed to a discrepancy in water density between different layers of Mirror Lake. This discrepancy has disrupted the natural spring mixing cycle and created low-oxygen conditions that reduce the habitability of the lake for its lake trout population.

“The reduction in mixing from road salt puts the lake at greater risk of HABs. We will continue to work with our partners at AWI to understand what led to this incident,” Ausable River Association Executive Director Kelley Tucker said in a statement Tuesday. “Our work on salt reduction, stormwater improvement, and other measures to protect Mirror Lake is more important now than ever.”

Wiltse has said the mixing cycle can be restored if road salt application is reduced by 30 to 40%. State, village and town officials have taken a number of steps over the years to curb road salt use on Mirror Lake Drive and surrounding areas. An upcoming multi-million-dollar infrastructure overhaul on Main Street is in part designed to mitigate the amount of road salt entering Mirror Lake.

Mirror Lake did “turn over,” or mix its cold bottom water and warmer top water this year; in other recent years it did not.

“AWI field scientists sampled the lake on Friday and noted that it had turned over, a natural process that occurs in the fall that can bring nutrient-rich water from the bottom of the lake to the surface, possibly contributing to the HAB event,” Wiltse said. “The unseasonably warm, sunny weather over the last few days may also be a contributing factor. Thankfully, we have a robust monitoring program that not only helped detect this early but will provide data critical to further our understanding of the circumstances around this bloom.”

Those who see a harmful algal bloom should submit a form to the DEC. Visit www.dec.ny.gov/chemical/77118.html to find out more about how to spot these blooms and how to report them.

A harmful algal bloom was also discovered for the first time on Lake George over the weekend, the Glens Falls Post-Star reported Tuesday. It was discovered along the shoreline in Harris Bay by a group of citizen scientists working with the state Department of Environmental Conservation’s Citizen Statewide Assessment Program.