Mirror Lake salt levels continue to drop

Adirondack Watershed Institute Senior Research Scientist presents preliminary data from the AuSable River Association and AWI’s study of salt levels in Mirror Lake. (Enterprise photo — Lauren Yates)

LAKE PLACID — Preliminary data from the Adirondack Watershed Institute reflects a further downshift in salt levels in Mirror Lake this year, which AWI Senior Research Scientist Brendan Wiltse said is likely a result of local salt reduction efforts.

Wilste, along with staff at the AuSable River Association, was excited to present good news with this year’s preliminary Mirror Lake data at Heaven Hill Farm on Thursday. The presentation was a preview of AWI’s final report, which has yet to be released, detailing the past year’s salt levels in the lake. The preliminary data shows that upgrades to the stormwater system in Lake Placid have had measured effects on salt reduction in Mirror Lake this past year, and Wiltse said salt use around Mirror Lake has gone down by around 9 – 12% following salt reduction efforts put in place in the town of North Elba and village of Lake Placid. Wiltse said salt levels in the lake started trending down in late 2019, but he said there’s still more work to be done.

Mirror Lake is the most “developed” lake in the Adirondacks, according to Wiltse, and it’s also one of the saltiest — only Lake Colby and the Cascade lakes exceed Mirror Lake’s chloride levels. Wiltse said that nationwide, excessive salt use often stems from the modern expectation that the roads should be as clear on a snowy day as on any other. He added that there’s a common story around the area that the 1980 Winter Olympics in Lake Placid were a big factor in kicking up salt use in the Adirondacks. But to most effectively protect Mirror Lake’s aquatic life and water quality, Wiltse estimated that salt use would need to be reduced by around 75% from current practices.

Salt concentrations are measured in milligrams per liter, and Wiltse said that Mirror Lake’s levels were at 4 mg per liter in 1974. Today, they’re at just over 40 mg per liter. Wiltse said that AWI’s overall goal is to see Mirror Lake’s salt levels get down to 10 mg, which would “really protect the lake.” That would require salt use to be cut down to a third of what it is now. For now, AWI has a goal of getting Mirror Lake’s levels down to below 40 mg. That would take a 3-5% reduction from current salt use practices, according to Wiltse.

On a parkwide scale, Wiltse points to the state Department of Transportation’s salting practices as the main problem. He said the state lays down the most salt per area, and while he hoped the state would be a “willing partner” in providing its salt use data for the AWI’s study — like the village of Lake Placid, which attached cameras to its plows so AWI could track the amount of salt being applied to roads — he said a Lake George group had to submit Freedom of Information Law requests for the state’s plow data and it took anywhere between 12 to 16 months for the state to return that information. Wiltse thought that the state’s road salt task force, which presented a preview of its final report and recommendations for salt reduction earlier this month, planned to recommend a 50% reduction in salt use parkwide.

Why salt matters

Mirror Lake completely turned over this spring for the first time since 2020, and for only the second time in the last five years. Mirror Lake failed to turn over in 2017, 2018, 2019 and 2021 because of a high concentration of salt in the lake — a direct result of road salt use, according to Ausable River Association Water Quality Associate Leanna Thalmann. Saltwater is dense and settles at the bottom of the lake, which can prevent mixing. This year, salt levels were lower and more storm events after Mirror Lake’s ice went out on April 14 helped the lake turn over.

Turnover is important for large lakes because the process replenishes oxygen and distributes nutrients throughout the lake. Turnover is a process that most lakes go through each fall and spring, according to the Ausable River Association. It’s the natural process of a lake’s cooler, dense water sinking to the bottom of the lake and mixing with deeper water. Water is at its densest at around 39 degrees Fahrenheit, so when the ice melts and the top layer of cold lake water starts to warm up a bit, it drops to the bottom of the lake and mixes with the deeper water.

In recent years, Mirror Lake’s turnover has been disrupted by high concentrations of salt in the lake. When a lake doesn’t turn over, there’s less oxygen on its floor, which can lead to several adverse effects on the lake’s biome — like algal blooms. If a harmful algal bloom spread across Mirror Lake, Wiltse said, people wouldn’t be able to swim or paddle in the lake. Turnover is especially important for rainbow and lake trout in Mirror Lake, which like to hang around in cooler water at the lake floor.


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