Ice rims part of Lake Auburn on Monday afternoon, blown toward shore from strong winds the past few weeks. On Wednesday, at least 90% of the ice was gone on the lake. Russ Dillingham/Sun Journal

AUBURN — Lake Auburn now experiences 30 fewer days of ice cover annually, on average, compared to 70 years ago, extending the growing season for algae, according to data from the Auburn Water & Sewerage Districts.

Maine’s water quality is particularly good, largely due to its cold climate, Scott Williams, former executive director of Lake Stewards of Maine, said in 2021. When the water is cold, algae doesn’t grow.

But data from the Auburn Water & Sewerage Districts indicates that as the state’s winters grow warmer, the periods of ice cover which protect the state’s lakes are growing shorter.

This year, it took until Feb. 1 for the lake to completely freeze over, the latest “ice-in” date for Lake Auburn since staff at the Auburn Water and Sewerage Districts began keeping track in 1953. According to Water Treatment Manager Christopher Curtis, ice-in on Lake Auburn is determined when the lake is completely covered by ice.

On Wednesday, the lake iced-out, meaning at least 90% of the lake was free from ice cover. In total, there were 70 days between ice-in and ice-out on Lake Auburn this year, the fourth shortest duration in 70 years.

It was 66 days in 2006, 68 days in 2012 and 63 days in 2021.

Diminishing ice cover is a point of anxiety for those tasked with managing the lake water. The less time the lake is covered in ice, the more likely the lake will have problems later in the year.

“We sleep better at night the longer the ice (is present),” Curtis said.

It’s not just ice cover, he added. Researchers at Bates College in Lewiston have found that the lake water is also becoming warmer.

There are other climate-related factors which impact the lake, Watershed Manager Erica Kidd said. Warmer temperatures mean more rain – as opposed to snow – during the year, washing more nutrients into the lake and creating ideal conditions for algal blooms in the summer and early fall.

Near Christmas last year, there was a major rainstorm in the watershed, she said. Hundreds of feet of Lake Shore Drive near Townsend Brook eroded into the lake. For months following the storm, lake monitors saw a decline in the clarity of the water, known as turbidity.

“(Major rainstorms) can be a big input of nutrients, specifically phosphorus,” Kidd said. “That is a long-term impact. I mean, once it’s in the lake, it’s in there. And so that can add to that additional algae growth later in the season.”

According to Kidd and Curtis, large rainstorms like the one in December can impact the water quality of the lake for years to come, especially because the water is slow moving. It takes more than two years for the lake water to completely change over, they said.

Large rainstorms like this have become more common in recent years, Curtis said.

Making matters more difficult, he added, is that sediment in the watershed is already naturally high in phosphorus content due to a mineral called apatite.

Amiyaha Graves, 9, of Lewiston jumps between rocks Wednesday on the edge of Lake Auburn. The Auburn Water & Sewerage Districts declared “ice out” for the lake on Wednesday. Graves, a fourth grader at Connors Elementary School, played on the edge of the lake with her mother, Ashley Smith, and cousin, Nakari Smith. Daryn Slover/Sun Journal

For now, Kidd said she’s focused on projects to improve drainage and reduce erosion near the lake. Since the washout on Lake Shore Drive, the state has pushed forward a project to widen the culvert for Townsend Brook to prevent similar problems. Still, it will likely be years before the project is complete, she said.

She also hopes to work with other towns in Lake Auburn’s upper watershed, namely, Turner, Minot, Hebron and Buckfield, to better understand how farms and development may be impacting the lake.

“Anything that’s lessening the amount of forest cover basically, it’s a concern whether that’s agriculture or it’s development,” she said.

A 2022 study found that Lake Auburn “reached a tipping point in the 2010s where key environmental thresholds were reached or passed,” specifying, among other things, that forest cover in the watershed had dipped below 75%.

The water district may again look to treat the water with aluminum sulfate when phosphorus levels get too high. The last treatment was in 2019. The chemical binds to phosphorus and settles to the bottom of the lake, making the nutrient less accessible to algae.

Recently, the Lake Auburn Watershed Protection Commission hired a consultant to identify sources of higher amounts of phosphorus in Lake Auburn. The group also suggested that another aluminum sulfate treatment may be needed in the lake as early as May or June this year.

“Obviously we want to do work in the watershed and get to the sources of these issues,” Kidd said. But there are those other in-lake or in-tributary treatments you can use too . . . I think, for us (it will) probably (be) a combination of those two things going forward, just watershed management and then in-lake management.”