Neighbors of Stillwater's Lily Lake celebrate decadeslong cleanup

It took decades of effort, government action, volunteers and "the world's largest rain garden," but neighbors of Stillwater's Lily Lake have been celebrating the restoration of the once-popular swimming spot.

The 41-acre lake spent 20 years on Minnesota's impaired waters list because of phosphorus-rich runoff and became notorious for the deaths of two children in 2010 and 2012 from an amoeba-induced infection.

Lily Lake's swimming beach remains closed, but lakeside residents and water quality experts say the many steps taken to restore the lake have paid off. It's time to think about Lily Lake's future, "to make Lily Lake the gem that it once was," said Mike Lyner, president of a group of local residents known as the Friends of Lily Lake.

The story of the lake's turnaround, and locals' hope for its future, was shared Wednesday at the Minnesota Water Resources Conference, a major water quality gathering in St. Paul.

The lake was removed from the impaired waters list in 2022 by the U.S. Environmental Protection Agency. Water quality tests show that clarity averaged about 16.5 feet last year, according to the Minnesota Board of Water and Soil Resources. That's far better than the lake's worst days of about 4 feet, Lyner said.

Back then, in the 1990s, lakeshore residents petitioned Stillwater to do something about algae and weed growth, Lyner said. Studies at the time showed how neighborhood runoff filled the lake with phosphorus. Found in dog waste, grass clippings, loose soil and other sources, phosphorus causes large algae blooms and reduces oxygen levels, choking off other life.

In 2013, the weeds had become so thick that paddling a kayak became difficult, Lyner said.

That's when neighbors created the group that would become the Friends of Lily Lake. They wanted to collaborate with the city, Lyner said. "We didn't go in screaming and complaining," he said.

The city agreed to build curbside rain gardens, and neighbors adopted them, agreeing to help clean them. Volunteers adopted storm sewer drains to clear debris, especially leaves and grass clippings. Lakeshore lot owners installed buffer strips of vegetation to prevent lawn runoff. The volunteer group Sustainable Stillwater organized buckthorn removal from nearby woods.

As neighbors organized, water quality experts ramped up their work.

Matthew Downing, administrator of the Middle St. Croix Watershed Management Organization, said the group did a small project in 2009, installing pervious pavers and a buffer of natural habitat and grasses next to the lake's public boat launch to filter runoff.

In 2015, the organization measured each source of water entering Lily Lake to determine the worst sources of phosphorus and other pollutants. The work helped steer the construction of a 36,000-square-foot filtration basin at the public launch to tackle the worst pollutants.

"It's the world's largest rain garden," said Angie Hong, the water education senior specialist for the Washington Conservation District.

The final step was to treat the lake using aluminum sulfate. The material binds with what phosphorus remains in the lake, clearing the waters. It can only be done once, said Downing, and it didn't make sense to use it when the lake was seeing fresh phosphorus pour in each year.

Those final two steps — the basin and the aluminum sulfate treatment — were paid for with a $513,000 Clean Water Fund grant, one of five such grants the state Board of Water and Soil Resources awarded to Downing's group for work on Lily Lake. The city of Stillwater provided a $70,000 match.

The basin, the alum treatment and other projects by the city, including 19 curb-cut rain gardens, prevent 145 pounds of phosphorus from entering the lake annually, according to the Board of Water and Soil Resources.

The lake is clean again, but Stillwater city engineer Shawn Sanders confirmed that the swimming beach remains closed, with uncertain plans.

The lake was the site of the deaths of 7-year-old Annie Bahneman in 2010 and 9-year-old Jack Ariola Erenberg in 2012. A Naegleria fowleri amoeba infected both children; their official cause of death was primary amebic meningoencephalitis. The amoeba lives in freshwater in the sediment of a lake bottom. If it's stirred up and enters a swimmer's nose, it can cause infection.

The children's deaths were not caused by the phosphorus contamination that put Lily Lake on the state's impaired waters list, although many people erroneously see the two events as connected, Hong said.

The naturally occuring amoeba was later found in six area lakes.

The amoeba presents a greater risk when hot weather warms up stagnant water, but even in those times it's extremely rare.

The Lily Lake cases are the only two known cases of fatal Naegleria fowleri infection in the Upper Midwest. The parasite is more common in Southern states and has caused some 154 cases in 60 years of monitoring, according to the U.S. Centers for Disease Control and Prevention.

The neighborhood wants to see the lake become a destination and has presented a 70-page long-term plan to city officials. It calls for a new recreation center, perhaps with an indoor pool, on the site of the existing ice arena, along with improved walking trails, expanded native and pollinator plantings, an outdoor education area and other amenities.

City Council Member Mike Polehna said Stillwater has taken some of the steps the group has requested: upgrading the boat launch, erecting more signs and changing traffic flow. The playground at Lily Lake is being redone next year as well.

"The feasible things we've tried to do already," Polehna said.

The City Council is not now discussing the more expensive items, including a new rec center and an awning over a portion of the parking lot.