$1.4 million Mirror Lake improvements should finish this winter


courtesy of Rice Creek Watershed District • St. Anthony’s Mirror Lake will be new and improved after this winter, with greater flood capacity to better contain water and pollutants, as well as a re-made shoreline.

Mirror Lake is man made, constructed in 1962 to provide flood protection and to store water. 

Ever since, polluted farm and stormwater runoff from some 240 acres of surrounding urban land has filled the lake with sediment, diminishing its flood-storage capacity and threatening bodies of water downstream with pollutants like phosphorus, which causes algae blooms.

The summer of 2011 made clear that Mirror Lake, located just north of Wilshire Park Elementary on the border of St. Anthony and New Brighton, needed updating, when a storm left some nearby St. Anthony homes and cars underwater. 

The $1.4 million Mirror Lake project, carried out and paid for by the City of St. Anthony, along with help from a Clean Water Fund grant and the Rice Creek Watershed District, was scheduled to be completed last winter. But, due to warm winter conditions like rain in February, about 20 percent of the project was left undone, according to St. Anthony City Manager Mark Casey. 

The remaining Mirror Lake improvements should be finished this winter. 

The project will add some 12 million gallons to the lake’s flood capactiy and reduce phosphorus and algae contamination. The lake will also be outfitted with a bench surrounding its perimeter as a public safety precaution.

Casey said the lake has a deep drop-off. “We deemed it kind of unsafe,” he said, adding that the safety bench makes the drop off not as deep. 

A buffer strip of native, pollinator-friendly plants will surround the lake and the growth of native aquatic plants will be reestablished in the lake. 

The work requires a hard freeze, said Casey. Remaining, unfrozen water is drained from the lake. The bottom of the lake is then dredged to add flood storage.

Following the flooding of 2011, Casey said he and city staff began working with affected residents to come up with a solution. Adding more storage to Mirror Lake became the priority. 

Extra flood storage is also beneficial to water quality, said WSB & Associates employee and St. Anthony City Engineer Todd Humber. 

Water from Mirror Lake, which has been high in sediments for the last 50 years, flows through Pike Lake, Long Lake and Rice Creek out into the Mississippi River. When there is more water storage space, Humber said, water doesn’t move in and out of the lake as quickly. As the water sits, sediments — which can include pollutants such as phosphorus — sink to the bottom of the lake instead of traveling with the water to the next stop. 

“It’s kinda like Kool Aid,” Humber said — when Kool Aid is left to sit in a glass, the Kool Aid mix sinks to the bottom. “We want that.”

Putting pollinator-friendly vegetation along the outside of the lake also naturally filters water before it reaches the lake, said Humber, adding that he and the city are working on a variety of trees to provide habitat diversity for different animals and birds. 

The ring of native plants, targeted toward bee and butterfly species, also stabilizes the shoreline from erosion, Humber noted. 

Project costs were covered by $640,000 from a Clean Water Fund grant, $502,000 from the watershed district and $250,000 from St. Anthony.

With winter coming and the needed deep freeze seemingly immenent, Humber said the project has only a few more weeks left of work.


 

– Solomon Gustavo can be reached at sgustavo@lillienews.com or 651-748-7815.

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