Fish Lake is a 232-acre recreational lake in Maple Grove, MN with a maximum depth of 61 feet. The lake is eutrophic with summer algae blooms that can result in odors and unsightly build-up of algae along the shorelines. It is the concentration of phosphorus which controls the level of algae growth. Lake water column phosphorus concentrations now average above the State of Minnesota’s phosphorus standard.
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. Samples from the bottom of the lake confirmed that phosphorus was very high in the sediments and available to be released into the overlying water column. HAB Aquatic Solutions conducted the first of two planned alum applications in September of 2017 and we are happy to be back for the second and final round! We will apply the second dose of 95,000 gallons of alum over a five-day period in August of 2019. The application produces a “floc” that settles to the bottom of the lake. The floc has sites where phosphorus in the sediments become chemically 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 potential toxins and improve the recreational opportunities for lake users.
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