A view of Route 4 and the public boat launch on Lake Auburn in 2017. Russ Dillingham/Sun Journal file photo 

AUBURN — The results of a comprehensive study of Lake Auburn will likely revive talks over the future of Lake Auburn, including whether recreational swimming should be allowed.

A study commissioned by the City Council says the city could develop a recreational swimming area, but recommends that it be a roped off section of the lake with a 50-person capacity.

Swimming and other recreational uses of the lake except for boating have been prohibited for decades. Officials said the study, which will produce a full report in July, could lead to a small “pilot program” to test the impact from swimming on water quality.

The debate between watershed protection efforts and the potential for more recreation on the lake has been amplified over the past few years, as the lake has dealt with algae, warming temperatures and other water quality questions.

Mayor Jason Levesque said Tuesday that the study results provide a level of data that municipalities “rarely” have access to make educated decisions.

“I do believe this is the dawn of a new era in Auburn,” he said. “Where we actually have actionable data that we can use to influence the future of our city and build something that’s economically sustainable, ecologically sound, and something that creates recreational opportunities for all our residents.”

Due to historically clean water at the lake, the district has received a waiver of filtration since 1991, which allows it to treat the water with ultraviolet light and other means without having to pay to filter it. But it must continue to meet certain water quality standards to maintain the waiver.

The city hired FB Environmental, along with the Horsley Witten Group and the University of Maine to conduct the $100,000 study earlier this year. The project analyzed the environmental, economic and regulatory impacts of water protection in the Lake Auburn watershed.

The study, presented for the first time Tuesday at a council workshop, used a computer model to quantify the delivery of phosphorus, a nutrient known to cause or exacerbate algae blooms and cyanobacteria in lakes. It used several models to predict water quality conditions up to the year 2100.

Rich Brereton, project manager for FB Associates, described the two models used in the study. One looked at development and other changes within the watershed based on “business as usual,” meaning with no changes to current restrictions around the lake. The other looked at “maximum development,” if rules were relaxed.

The simulation estimated that based on “business as usual,” there would be some new development, including in the upper watershed areas of Turner and Minot. The model projects that by 2100, the average annual phosphorus in the lake would be 9.5 parts per billion, close to a threshold of 10 parts per billion that Brereton said leads to the kinds of algae blooms that have plagued the lake in the past, but still not likely of violating the district’s filtration waiver.

He said that number also takes into account regular use of aluminum sulfate, a treatment that has been used by the watershed as recently as 2019, to cut down on phosphorus.

Under the “maximum development” model, the phosphorus levels are projected to reach an average of 10.7 parts per billion, meaning an 80% chance of algae blooms in the lake. Under that model, Brereton said a violation of Auburn’s filtration waiver is likely.

He cautioned the council that there is uncertainty in the modeling, particularly due to climate change. Prior to the recent aluminum sulfate treatment, the phosphorus level was 10.9 ppb. Last year, it was down to 8.3 ppb, meaning algae blooms are unlikely.

Looking at the economic impact, the study predicts that the “business as usual” approach, but with some added recreational uses like swimming, also yields more positives. That model predicts a $1.2 million total benefit, while “maximum development” is $190,000.

Brereton said the study suggests “identifying ways to expand development opportunities that would minimize impacts on water quality.”

That means “low impact development,” that employs rules like reducing land clearing on sites, limiting the size of impervious areas, and using vegetated buffers.

“With appropriate restrictions, it should not have an adverse impact on the phosphorus situation in the lake,” he said, regarding swimming. But, he said, the recommendations include no swimming allowed from boats, and using paid stickers to ensure funding for water quality monitoring.

He said “losing the waiver is not inevitable,” but said Auburn should set clear community goals. Key thresholds to keep in mind, he said, are the 10 parts per billion for phosphorus, and keeping the watershed at least 75% forested.

Other city officials were also positive, including Councilor Holly Lasagna who said, “This has been a really thorny issue for a long time. This shows us a path forward that we haven’t had.”