Salt success: How Lake Placid rallied to save Mirror Lake

Community’s efforts to reduce salt use, divert runoff has helped bring key Adirondack lake back from the brink

By Zachary Matson
When scientists 10 years ago started monitoring salt pollution in runoff flowing into Mirror Lake, they discovered their sensors were measuring chloride concentrations similar to those found in seawater.

At that time, nearly two dozen stormwater outfalls channeled road runoff directly into Mirror Lake. There was little to slow or stop water rushing off all of the village of Lake Placid’s hard surfaces, collecting debris, sediment and road salt along the way. The lake’s watershed mirrored conditions found in urban environments. More than one-quarter of the lake is ringed with development—even if its background is protected wilderness.

Researchers with the Ausable Freshwater Center (at the time known as the Ausable River Association) monitored the outfalls to measure pollution levels in the runoff. How salty was it as it reached the lake? At one site, their sensors measured chloride concentrations of 12,000 mg/l, so high it effectively reached the limit of what the sensor could measure.

“This is many thousands of times higher than what we would expect to see flowing into an Adirondack lake,” said Brendan Wiltse, who led research on Mirror Lake for nearly a decade. “We needed data loggers calibrated for seawater.”

The problem in Lake Placid grew so severe that salt loads were disrupting Mirror Lake’s natural turnover, an important biannual occurrence that mixes nutrients and oxygen and reinvigorates zones of fish habitat. Scientists estimated that at one point in 2017, the preferred oxygen levels for lake trout had been squeezed entirely from the lake.

But coordination between researchers monitoring the lake and local leaders helped reverse the salt concentration trend line. Through an adoption of snow management best practices, an infusion of state money and a major infrastructure overhaul, the efforts have reduced salt use and redirected runoff away from Mirror Lake.

In the past few years, salt concentrations fell below a targeted threshold and the lake is mixing again. Advocates hope to grow public awareness and rein in salt use on private parking lots, driveways and sidewalks by encouraging more residents and contractors to use less.

A salty problem

A scientist assessing Mirror Lake in 1974 recorded chloride concentrations of 4 mg/l, notably higher than the less than 1 mg/l expected in untouched Adirondack lakes. By then Mirror Lake sat at the heart of the village at the heart of the Adirondacks. But very little data on the lake’s chloride concentrations was collected in the ensuing decades, even as state and local road salt use exploded in the wake of the 1980 Winter Olympics. By the time Wiltse and colleagues ramped up regular sampling of the lake in 2015, chloride concentrations were 10 times greater, 40 mg/l, a level researchers have found to harm aquatic life.

Scientists expect Mirror Lake to undergo mixing events in the spring and fall, as water temperature and density trends toward equilibrium and distinct water layers combine. The river association enrolled Mirror Lake in the Adirondack Lake Assessment Program, which documents chloride concentrations and started collecting water samples every two weeks. Sampling included profile measurements that reveal different chloride and oxygen levels at various depths—an indication of internal lake dynamics. During his first sampling visit to Mirror Lake in May 2015, Wiltse was distressed by what he found.

Related reading: DOT announces pilot programs to reduce salt on Mirror Lake and Lake George

“I observed very low oxygen in the lake and very high conductivity,” Wiltse recalled. Researchers use conductivity as a proxy for salt levels. “The lake should have mixed a month earlier, there should have been plenty of oxygen. It raised some red flags.”

The data signaled a troubling reality. By that time of year, the lake should have started to mix and the oxygen and conductivity measurements should have been relatively consistent throughout the water column. Instead, as soon as Wiltse pulled his sensor from the water and recorded its readings, he theorized that chloride concentrations were building up in the lake depths and interfering with the annual spring turnover, exacerbating oxygen loss. The low oxygen levels threatened Mirror Lake’s lake trout and its overall water quality.

Excessive salt use had stopped the lake from mixing.

“That was my hypothesis when I was on the water,” Wiltse said. It took another four years to prove it.

Wiltse and his colleagues between 2015 and 2018 measured average chloride concentrations of 44 mg/l at the water surface, while clocking average concentrations of 65 mg/l at the lake bottom. The bottom concentrations increased throughout the winter, as more and more salt ran off Lake Placid roads.

In 2019, they published an article documenting the salt-induced disruption of the lake’s natural turnover. Peer review had spoken: Mirror Lake earned the ignominious distinction as one of just a handful of lakes to experience that level of disruption.

Mirror Lake is a bit of an odd duck when it comes to Adirondack lakes and may well be the park’s only urban lake, according to land use definitions.

The lake is entirely surrounded by state and local roads and includes one of the most developed shorelines of any in the park. Its 740-acre watershed contains over 1,000 meters of state highway, salted three times as heavy as other roads, and over 4.5 miles of local roads. Nearly 70 acres of paved surface, including 20 acres of parking lot, funnel stormwater and snowmelt toward the lake.

“It shows when you have a lake of this size, in this setting, what salt can do to it,” said Bill Billerman of the Mirror Lake Watershed Association.

Lake Placid’s Main Street, maintained jointly by state Department of Transportation plows and local highway crews, hosts thousands of winter tourists each year, and businesses rely on clear sidewalks and parking lots.

Related reading: Mirror Lake progress highlighted at annual salt summit 

To keep snow from building up along Main Street, the village of Lake Placid highway department maintains two snow fields, where crews deposit snow hauled from downtown. A fleet of sidewalk sweepers keep walkways clear. As a December snowstorm started to form near Lake Placid, Brad Hathaway, the Lake Placid’s superintendent of public works, planned for a team of workers to clear downtown beginning at 2 a.m.

State plow drivers clear Main Street’s driving lanes, pushing snow toward the parking lanes, before the village crews clear the parking spots and sidewalks, load snow into dump trucks and haul it away. It would take 15 workers around four hours to clear Main Street and side streets, Hathaway said.

“It’s a much different operation here,” he said. The goal is to keep the sidewalks clear of snow—even when the snow refuses to stop. “It’s a constant effort.”

As Wiltse and his colleagues collected more and more data on the consequences of salt pollution on Mirror Lake, they kept local leaders in the loop and helped advise on ways to reduce salt use. The river association coordinated grants to support equipment purchases and continue intensive water quality surveillance, including a weather station collecting continuous information on lake conditions.

“From the moment of that first test we knew there was a problem, and there was no reason not to pay close attention to the threat,” said Kelley Tucker, executive director of the Ausable Freshwater Center.
Lake Placid and the town of North Elba, which also maintains roads in the watershed, invested in more effective plow blades and salt tracking devices.

The village upgraded its sidewalk sweepers and switched from spinners that spread salt widely to a more controlled dropper. “On the old ones, half the salt went into the road, half went into the buildings and a little was left on the sidewalk,” Hathaway said.

Wiltse spent years offering updates on the science at local meetings.
“Once they understood the problem as well as we did, the conversation shifted to, ‘OK, what can we do about this?’” he said. “My fundamental belief is that highway departments don’t want to be doing harm to the lake. Going in and pointing fingers and being adversarial never made sense to me.”

Rerouting runoff

The village had been planning a major overhaul of Main Street infrastructure for a decade, and local leaders saw the upgrades as an opportunity to slow the flow of salt-contaminated runoff into the lake.

With Main Street ripped up in 2021 and 2022, construction crews installed a trio of large retention basins—underground domes about the size of four school buses—one underneath Brewster Park at the end of Main Street and two underneath downtown parking lots. Stormwater flows into the basins and slowly infiltrates the groundwater, rather than running directly to the lake.

“The winter before the retention basins went in, you can see huge spikes in conductivity all winter long,” Wiltse said of the salt monitoring data. “The winter after those spikes all but disappeared.”
Driving north on Main Street, drivers reach a left bend where Main Street splits with Mirror Lake Drive, turns back to State Route 86 and climbs a steep hill. The hill section presented a tricky challenge to drivers, a challenge often treated with a thick layer of road salt. The road improvements included a subtle adjustment to bank the road and soften the 90-degree turn, so drivers can maintain more momentum through the turn, and road crews can drop less salt in the trouble spot.

Phil Snyder, who leads water quality monitoring at the freshwater center, said the lake has seen a reduction in chloride levels in recent years, a sign that strategies to reduce salt use and the Main Street overhaul are paying dividends. Chloride dropped below 40 mg/l, a goal the researchers and local leaders had set, but the concentrations remain high. A more ambitious goal of reducing concentrations to 10 mg/l would require far more significant salt reductions and time to flush away salt that has accumulated in soils and groundwater over many years of use. Concerns remain about the buildup of salt in the retention basins and groundwater, posing a different kind of lurking threat.

“If you start applying real solutions to these problems, you can affect them quickly in some places,” Snyder said. “The lake is behaving in a more natural state, but it’s teetering on that line.”

Putting students to work

Marie McMahon still tears up when she tells the story about the moment she decided to get off salt.
McMahon and her partner Wes Schock run Fire Side Wood, a landscaping, firewood and snow removal business in Lake Placid, and an employee called her out to one of their sites. The employee had used an entire 50-pound bag of rock salt on just over 400 feet of sidewalk—far more than the d shovels and brines osage suggested on the back of the bag.

“He only needed, if you did the math, 22 cups,” McMahon said. “When I saw the sea of green all the way down the walkways, I literally burst into tears. In that moment, I realized we were contributing to the problem.”

McMahon set out to use more chloride-free approaches after the realization of her own contribution to Mirror Lake’s salt pollution. “I didn’t know how. I just knew that was the goal,” she said. “If we have the privilege of living here, we also have the responsibility of taking care of this place.”

Marcy Fagan, chair of the Mirror Lake Watershed Association and a science teacher at Northwood School, saw a teachable moment in the story of Mirror Lake.

Fagan used the backyard example to help students understand why and how lakes mix and the ways human activity can disrupt natural processes. Working with McMahon, Fagan started to introduce her students, and the campus, to the gritty work of reducing salt use.

She divided students in her Adirondack science classes into groups charged with the responsibility to keep certain building entrances on campus clear of snow. Get out the shovels, students.

First, they mapped the campus, researched appropriate salt loads and coordinated with the school’s facilities director. McMahon is helping with a chloride-free brine as the students aim to lessen the salt the school puts into the watershed.

“It’s more exciting for them to be out doing,” Fagan said. “We still have a lot of salt in the water. It’s getting better, but we still have a long way to go.”

McMahon has a contract to keep the parking lots and sidewalks clear of snow at the Olympic Training Center in Lake Placid, where they are working to finetune their practice. She uses chloride-free brine on sidewalks and tested a half dozen shovels to see which worked best. She hopes to add cameras to the lot that record weather conditions and offer insight into how much snow has fallen.

McMahon is seeking to build a niche as a snow removal contractor mindful of salt’s negative impacts, while sharing what she learns with others. She said she has heard from caretakers of large camps around Mirror Lake interested in the approach.

“If people become aware there is another way, they will demand it,” McMahon said.

McMahon said she is encouraged by signs of progress but still wants to see the state do more to contribute to the solution. “If private contractors and municipalities can make it happen against the odds, I have a question for DOT: What the hell?”

Top photo: Ice begins to form on Mirror Lake in November 2017. Photo by Brendan Wiltse