Shields Lake Project Description

Shields Lake is 30-acre lake in the City of Forest Lake, MN.  The lake eventually flows to Forest Lake and it has a watershed that is 538-ac in size.  The lake is eutrophic, experiences excessive summer algae blooms, and has poor water quality (high phosphorus concentrations, large amounts of algae, low water clarity), and has been on the State’s Impaired Waters List for high nutrients since 2006.   A substantial amount of phosphorus has accumulated in the lakebed sediments over the years. The sediments release the phosphorus when oxygen levels decrease at the lake bottom.  This leaching of phosphorus from the lakebed is called “internal loading” and ultimately increases the amount of phosphorus available for algal uptake and growth.

HAB Aquatic Solutions will conduct a buffered alum application over a 2-day period in October, 2019.  The application produces a “floc” that settles to the bottom of the lake.  The floc has areas where phosphorus in the sediment becomes bound as it leaches from the bottom.  The floc effectively intercepts and binds the phosphorus, which makes it unavailable for the algae to use for growth.  The goals of the project are to dramatically reduce the internal loading of phosphorus from the sediments, lower the amount of phosphorus in the water column, reduce the amount of algae and improve the recreational opportunities for lake users.  The 2019 alum application will be the first of two, with the second scheduled for fall of 2020.

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