Brendan Wiltse, the senior research scientist with the Paul Smith’s College Adirondack Watershed Institute, said both people and their pets should avoid contact with the water of Mirror Lake. Harmful algal blooms — or HABs — can contain toxins that can make people, pets and wildlife sick. While Wiltse said the AWI isn’t sure if the HAB on Mirror Lake contains toxins, he said people should keep away from the water for at least the next several days.

HABs thrive in warm, sunny and calm conditions — the kind of weather that residents and visitors enjoyed last week. Wiltse said he still saw patches of the HAB on Mirror Lake Wednesday morning, Nov. 2, and he said toxins from HABs can persist in the water even after the bloom dissipates.

If humans or animals touch or swallow water with harmful algal blooms — or inhale airborne droplets — they may experience adverse health effects, according to the 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.

The bloom was first reported by people who were hanging around Mirror Lake on Halloween and saw what they thought was a HAB, according to Wiltse. The AWI later went out on Mirror Lake and sampled and confirmed the bloom. The state Department of Environmental Conservation Harmful Algal Bloom Program also confirmed the bloom and added it to the state database.

This year’s bloom is the same species of cyanobacteria — blue-green algae that can produce toxins — that bloomed on the lake at the beginning of November in 2020, according to Wiltse. But based on the AWI’s 2020 data and reports, this year’s bloom is larger than the last reported bloom. When the AWI went out to sample the bloom on Halloween, Wiltse said it was “widespread across almost the entire lake.” Cyanobacteria occurs naturally in the lake, according to Wiltse, but concerns about toxicity arise when dense blooms form.

There isn’t one clear culprit to blame for this year’s bloom, Wiltse said, but the AWI is studying the multiple factors — like lake turnover, climate change and road salt use — that could be contributing to the bloom’s appearance.

The 2020 bloom was “strongly tied” to the lake turning over just prior to the bloom, according to Wiltse, and he thought that could be part of the reason for this year’s bloom. Turnover is a process that most lakes go through each fall and spring when the lake’s cooler, dense water sinks to the bottom of the lake and mixes with deeper water. The turnover process brings nutrients that were trapped in the lake’s deeper water up to the surface, according to Wiltse. Those nutrients combined with the warm, sunny days are the recipe for an algal bloom, and Wiltse said that’s “likely” what caused this bloom — he said that Mirror Lake is in the process of turning over, so some nutrients are currently rising to Mirror Lake’s surface waters.

“But we won’t be able to say anything definitively on that until probably early next year, once we finish all the data collection for the lake and have a chance to analyze everything,” Wiltse said.

When it comes to cleaning up a HAB, Wiltse said there’s nothing to do but wait until it passes. In terms of long-term HAB prevention, Wiltse said it’s important to keep studying what triggers blooms to better understand what can be done at a water management level to reduce the chance of future blooms.

“In general though, anything that we can do to be better stewards of our water bodies is going to reduce the likelihood of something like this happening,” Wiltse said.

Wiltse mentioned reducing the use of pesticides and fertilizers on lawns and reducing road salt use as bloom prevention methods. The village recently revamped its stormwater system, and Wiltse hopes that will improve the runoff of road salt and excess nutrients that can drain into Mirror Lake.