About the Lakes

Eagle and Pike Lakes in Maple Grove and Plymouth, Minnesota are Impaired Waters for excess nutrient concentrations (phosphorus) that contribute to algae blooms and poor water quality in the summertime. The Shingle Creek Watershed Management Commission is taking a multifaceted approach to improve water quality in the lakes, including:

• Watershed Best Management Practices (BMPs; ex, rain gardens, stormwater infiltration practices)
• Internal load reduction via alum treatments
• Invasive aquatic vegetation delineations and herbicide treatment
• Commission and volunteer water quality and aquatic vegetation monitoring
• Shoreline restoration workshop for lake residents​

​As part of a joint lake management plan, both Eagle and Pike Lakes will receive two alum treatments. The first treatment is planned for Fall of 2024, and the second will occur 1-2 years later. We expect an immediate improvement in water clarity, and a significant reduction in phosphorus release from the sediments following the alum treatments. The project also includes treatment of invasive curly-leaf pondweed and Eurasian watermilfoil.

This project is the result of the recently completed Eagle Lake Subwatershed Assessment, which evaluated watershed phosphorus loads to Eagle Lake and internal loads in both Eagle and Pike. The study recommended internal load management via alum treatments in both lakes.

Proposed Project Timeline

What is internal load?

Excess phosphorus comes both from the watershed (runoff) and from the lake sediments. When water on the bottom of the lake becomes low in oxygen, typically in mid- to late summer, a chemical reaction occurs that releases bound phosphorus from the sediment to the water column. The most common method of reducing this "internal sediment release" is to apply aluminum sulfate (a.k.a., alum) to the lake. The liquid alum slowly filters down to the lake bottom. As it falls, it binds with phosphorus in the water column to form a floc. That floc settles on the bottom and forms a protective barrier between the sediments and the lake, inhibiting the further release of phosphorus.

For more information on alum treatments, check out the MPCA's Lake protection and management website.