Case Study: Alum Application Restored an Impaired Lake


Alum Application Improves Water Quality and Removes Lake from "Impaired" Water List

Fish Lake is a 232-acre recreational lake in Maple Grove, MN with a maximum depth of 61 feet. The lake was eutrophic with summer algae blooms that resulted in odors and unsightly build-up of algae along the shorelines. Elevated phosphorus (P) levels (above Minnesota’s P standard) historically drove the excessive algal growth. Fish Lake samples confirmed that phosphorus was very high in the sediments and released into the water column via internal loading.

Local leaders decided to move forward with the water restoration solution, alum. Through our alum applications, this lake was removed from the “impaired” water list!

Applying Alum to Restore Water Quality

HAB Aquatic Solutions applied half the total alum dose (95,000 gallons) in over 5 days and the remaining half dose (95,000 gallons) over a 5-day period a few years after the initial application. Phosphorus levels were monitored between these two applications and alum’s affects have continued to improve water quality levels.

The Results of Alum

The alum floc has been successfully inactivating sediment P, reducing internal loading, lowering water column P, reducing algal biomass and increasing water transparency since the first application in 2017. The figure below shows the water column improvement in terms of water column TP, chlorophyll a and Secchi depth.

Note: phosphorus levels and overall water quality and clarity have improved over the years, leading to Fish Lake being removed from the “impaired” water list in 2024.

Want to learn more about Fish Lake's journey?

Click here to learn how Fish Lake’s “impaired” water status was removed.

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