Mirror Lake salt levels drop again

Brendan Wiltse leads students from Curt Stager’s Paul Smith’s College paleocology class across the ice of Mirror Lake in 2017 after the group collected a sediment core from the lake bed to test the DNA of deceased fish species decomposed into the soil beneath the lake. (Enterprise file photo — Antonio Olivero)

LAKE PLACID — Scientists have found that the concentration of salt in Mirror Lake dropped again in 2021, the second year in a row salt levels have decreased in the lake.

Brendan Wiltse has been studying Mirror Lake’s water quality for years, first as science and stewardship director for the Ausable River Association and now as a scientist with the Adirondack Watershed Institute. Studies and papers from both groups have revealed that Mirror Lake’s salt levels are higher than average due to road salt.

Mirror Lake is what’s called a “dimictic lake,” which means that its natural mixing process — when water cycles from its surface to its floor — happens twice per year, once in the spring and again in the fall. Salt contamination has disrupted the lake’s turnover in the past, impacting the lake trout habitat and putting the lake at risk of developing algae blooms. Studies of the issue have led to salt reduction efforts in the village of Lake Placid and town of North Elba. Now, Wiltse said, salt concentrations in Mirror Lake are consistently dropping.

In 2020, there “was a definite reduction in the amount of salt in the lake compared to the severity of the winter,” Wiltse said. And in 2021, there “was an even further reduction.”

Wiltse said he’ll know more about why the salt levels are dropping this spring, but he said that analyzing road salt use, weather conditions, consistently warming winters and how those factors are impacting salt in Mirror Lake could require years of data.

“We’re only starting to get that information,” he said.

Salt reduction efforts

Wiltse said it’s hard to know for certain why the salt levels are dropping — if it’s because of the salt reduction efforts or the warmer winters, with fewer weather events that require salting — and that he’ll know more about what led to the further reduction in salt this past winter as the spring progresses.

He said the AWI wasn’t tracking salt application data in 2020, so it’s also hard to say if the changes in salt management practices were a direct contributor to dropping levels that year.

Now, he said the town and village have “good data” on salt being used around the area to pair with this year’s study. He added that the Ausable River Association is putting out a salt survey to businesses and residents, which he hopes will provide a more complete picture of how road salt application is impacting the lake’s salt levels. It’s going to take a little longer to say with any certainty that the salt reduction efforts are driving the drop rather than consistently warmer winters, according to Wiltse. The salt survey is online now.

Wiltse said he has seen the most significant reduction in salt in Mirror Lake in recent history over the last two winters. He said 2015 and 2016 had low salt levels, but he said those were warmer winters with less snow and ice events. Now, his group is seeing consistent falling trends in the salt concentration despite colder winters.

Wiltse said that the amount of snowfall and the amount of salt in the lake are often related, and the number of severe weather events that require salting can directly inform how much salt is getting in the lake. “Starting in 2020, we started to see less salt in the lake for a given amount of snowfall that was happening in Lake Placid,” Wiltse said, “which is an early indication that the salt reduction efforts around Lake Placid may be having some success, but we need more data.”

Wiltse added that he’s excited to see how new improvements to the village’s stormwater system will influence the amount of salt in the lake. Part of the Main Street overhaul included a new water catchment system. All of the rainfall runoff around Lake Placid used to be directed to Mirror Lake through multiple outlets from the village’s stormwater management system, according to Department of Public Works Superintendent Brad Hathaway. Now, rainfall seeps through porous asphalt and into the water catchments, which will hold the runoff in a basin until the basin eventually absorbs the water. Hathaway said that the runoff would only enter Mirror Lake is if there was a “torrential” rainfall.

Wiltse said his group is interested to see how the new system, combined with reduced salt use, will affect the water in Mirror Lake this spring.


Wiltse said Mirror Lake is unique because salt from the road builds up at the bottom of the lake, which can interrupt the lake’s turnover in spring. Turnover is the natural process of a lake’s cooler, denser water sinking to the bottom of the lake while the warmer water rises to the top. Turnover is important for large lakes because the process replenishes oxygen and distributes nutrients throughout the lake.

When a lake doesn’t turn over, there’s less oxygen at its floor, which can lead to a few adverse effects on the lake’s biome.

Mirror Lake failed to turn over in 2017, 2018 and 2019, according to Wiltse. He said the lake turned over again in 2020 due to a reduction in accumulated salt and an early spring that melted the lake ice faster than usual. Wiltse added that when the ice goes out early, the lake has more time to mix.

Wiltse said the lake didn’t completely turn over in 2021, even with the reduction in salt use. He said the ice melted at a more typical time, shortening the lake’s opportunity to mix.

Mirror Lake’s fish population includes smallmouth and rock bass, white sucker, pumpkin seed, yellow perch and brown bullhead. The state Department of Environmental Conservation regularly stocks the lake with rainbow and lake trout.

Rainbow trout and lake trout like to seek cooler, well-oxygenated water in the summertime, and a lack of oxygen there could inhibit a healthy presence of those species in the lake. When the bottom of the lake goes for long periods without oxygen and then partially mixes, Wiltse said, the lake is at risk of developing harmful algal blooms. Phosphorus that was bound to the lake’s bottom would be leached into the water above and increase the risk of phytoplankton, which could form an algal bloom that produces toxic conditions for wildlife, people and pets. Wiltse said that kind of an algal bloom hasn’t happened yet, though one was spotted for a brief period on the lake in 2020.

Salt survey

One way people can help the salt data collection process is by filling out the AsRA’s and AWI’s salt survey funded by the Lake Champlain Basin Program. The survey is for people who live in the Chubb River watershed, which encompasses Lake Placid, and is intended to gather more information about the amount of salt entering Mirror Lake and Chubb River. The survey takes around five to 20 minutes to complete, depending on the size of the area being cared for in the winter, according to AsRA. If you aren’t sure if you’re located in the Chubb River watershed, email salt@ausableriver.org.


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