New project aims to take Lily Lake off the impaired water’s list

If you live in Stillwater, you’ve probably noticed the construction equipment and excavation work underway at Lily Lake Park along Greeley St.. This month, City of Stillwater and the Middle St. Croix Watershed Management Organization (MSCWMO) began constructing what might be best described as “the world’s biggest raingarden.” This regional infiltration basin will collect and filter stormwater from a large area of land that includes commercial and residential property, delivering it to Lily Lake cleaner and with less phosphorus.

After working for years to reduce stormwater runoff to Lily Lake through raingardens, gully stabilization projects, stormwater pond retrofits, and volunteer clean-up activities, this final project is expected to capture enough phosphorus to allow Lily Lake to be taken off of the state’s impaired waters list.

Matt Downing talks about the regional infiltration basin currently under construction near Lily Lake in Stillwater.

A brief history of water quality in Lily Lake

Step back in time to 1962, and you’d find Stillwater’s Lily Lake beach crowded with swimmers. Though small, Lily Lake was considered to be one of the deepest and clearest lakes in the Twin Cities area, much like Square Lake today. People from around the region came to Lily Lake to swim, relax, and enjoy sunny summer days.

Lily Lake beach in 1962.

Things began to change during the 1970s and 80s when new homes, roads and businesses were built on what was then the west side of Stillwater. To avoid flooding, road engineers directed stormwater runoff from these new developments into Lily Lake and, over time, water quality began to decline.

In 1998, local citizens launched a “Save Lily Lake” campaign focused on keeping stormwater runoff – and the sediment and nutrients it carries – out of Lily Lake. In 2006, a study conducted by the City of Stillwater and MSCWMO set a goal of reducing phosphorus flowing into Lily Lake by 145 pounds per year to prevent harmful algal growth and improve water clarity.

Tragedy struck in 2010 when seven year old Annie Bahneman died from a brain infection after swimming in Lily Lake, due to inhaling water containing a naturally occurring amoeba called Naegleria fowleri. Two years later, in 2012, nine year old Jack Ariola Erenberg died of the same infection after swimming in Lily Lake. The public beach has been closed since then.

Lily Lake improvement efforts

Over the past twenty years, City of Stillwater, the MSCWMO, community volunteers, and local government partners have implemented dozens of lake-improvement projects to benefit Lily Lake.  Projects have included stabilizing eroding gullies, redesigning the city-owned boat launch with porous pavers and native plants along the shoreline, installing raingardens in surrounding neighborhoods, retrofitting parking lots and stormwater ponds in commercial areas, and engaging community residents to adopt storm drains through the Adopt-a-Drain program.

Native planting near the fishing pier at Lily Lake Park.

The infiltration basin currently under construction will collect stormwater from the surrounding area, soak it into the ground, and deliver it to Lily Lake cleaner, and with less phosphorus. The project is expected to reduce phosphorus flowing into Lily Lake by 32 pounds per year, and will be the final step needed to achieve the 145lb phosphorus reduction goal set in 2006.

Next year, partners will conduct an in-lake alum treatment to bind phosphorus already in Lily Lake so that it can no longer feed algae. Says MSCWMO Administrator Matt Downing, “This is a great project that highlights how important it is to have implementation, education and outreach, and monitoring working together.”

Looking toward the future

The stormwater treatment projects in the Lily Lake watershed are designed to reduce phosphorus, a naturally occurring element found in sediment and organic materials such as leaves and grass clippings, and reduce algal growth. Naegleria fowleri may still be a concern in Lily Lake. However, it is possible that there will be less risk if the stormwater treatment measures lower water temperatures because the amoeba is more likely to become active in very warm water.

Ice skating on Lily Lake. Photo from Mike Lyner. The Friends of Lily Lake are currently working with the community to vision a new future for the lake.

The Friends of Lily Lake (formerly Lily Lake Association) is currently working with the city and community residents to envision a new future for Lily Lake and the surrounding parks and neighborhood. To learn more and share your thoughts in a survey, visit