Bald Eagle Lake Alum Treatment

City

White Bear Township, Hugo, and Lino Lakes

Completion Date

2016

Cost

$870,000

Phase

Complete

Water Body

Bald Eagle Lake

Funding Sources

Clean Water Partnership loan, Bald Eagle Lake Water Management District, Rice Creek Watershed District

Partners

Bald Eagle Lake Water Management District

RCWD worked with the Minnesota Pollution Control Agency (MPCA) to study the increasing levels of phosphorus, a nutrient that supports plant growth, in Bald Eagle Lake. When too much phosphorus gets into our lakes, it causes problems such as algae growth, low levels of oxygen for aquatic life, and murky water which makes it difficult for aquatic plants to grow. Once the study was completed, the RCWD used the information to identify a plan of action, which included applying aluminum sulfate to reduce phosphorus in Bald Eagle Lake.

RCWD applied two aluminum sulfate (alum) treatments to Bald Eagle Lake in the spring of 2014 and 2016. Alum binds to phosphorus, making it unavailable to algae, thus limiting algae growth.

While the RCWD believes this is an important first step towards improving water clarity and quality in the lake, applying alum does not address the nutrients washing into the lake during future rain events. RCWD is working with landowners and private partners to install projects that capture, absorb, and filter rainwater before it reaches the lake to minimize this problem in the future.

The alum treatment resulted in a 67% decrease in phosphorus and a 69% decrease in algae growth while water clarity improved by 63%. This resulted in enhanced water clarity (more than 5 feet) and advanced vegetation growth. From 2001-2008, readings for water clarity (Secci disk readings as reported to the MN PCA) showed visibility down only 5 feet and often less in late summer. After the initial alum treatment in 2014, water clarity improved to 11 feet at the maximum, and after the second alum treatment in 2016, the maximum reading moved up to 16 feet.

RCWD was given national recognition from the North American Lake Management Society. In 2017, Bald Eagle Lake water quality was restored and met the state standards for nutrients, algae and clarity for the first time since 1980.

Project funding was provided by the RCWD, the Bald Eagle Lake Water Management District, and a Clean Water Partnership loan of $400,000 (paid by the Bald Eagle Lake Watershed Management District).