A sign, seen here Thursday, warns beachgoers about harmful blue-green algae blooms on the shore of Mirror Lake. (Enterprise photo — Lauren Yates)

LAKE PLACID — Scientists have confirmed the presence of a harmful algal bloom on Mirror Lake. This is the second bloom to be reported in the lake since 2020.

Brendan Wiltse, the senior research scientist with the 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, Wiltse said — the kind of weather that Lake Placid has enjoyed for the last few days — and those conditions are expected to continue here throughout the weekend. Wiltse said he still saw patches of the HAB on Mirror Lake Wednesday morning, 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 this week 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.

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Causes and culprits

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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 right now, 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.

Wiltse said the AWI is also studying the extent to which road salt use and climate change could have an effect on bloom formations in Mirror Lake — especially blooms occurring this late in the season. He recently co-authored a report with Paul Smith’s College professor and scientist Curt Stager showing that Adirondack falls are getting warmer, and he said those conditions are favorable for HABs.

“We can’t link this individual event to climate change,” Wiltse said, “but it is something we’re looking into more detail in the future to try and understand that connection better.”

Wiltse noted that it’s important to monitor how road salt use could contribute to the presence of HABs in Mirror Lake, where high concentrations of road salt have been found to interrupt the lake’s turnover. But Wiltse added that HABs can occur naturally, too — he’s seen blooms on ponds in the Adirondacks in watersheds that haven’t been developed like the Chubb River watershed, where Mirror Lake is located.

“It can be a natural process, climate change might play a role — so there’s sort of a lot of pieces to consider when trying to understand the bloom dynamics here in the Adirondacks,” he 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.

This is the second reported bloom on Mirror Lake, but Wiltse said it’s “very likely” that blooms could have occurred here in the past and have gone undocumented. He said bloom reports have generally increased in the Adirondacks lately, but that doesn’t necessarily mean the presence of blooms has increased. Wiltse believes that awareness of HABs has grown among scientists, state agencies and the general public in recent years, and people have a better idea of what to look for and how to report HABs.