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Como Lake Alum Treatment


Capitol Region Watershed District (CRWD) is committed to improving water quality in Como Lake, a beloved water resource in Saint Paul for over a century. Despite efforts to address the water quality in the lake over the years, decades of stormwater runoff and pollution have made a new Como Lake plan necessary.

The 70 acre Como Lake drains more than 1,711 acres of land in Saint Paul, Roseville, and Falcon Heights. With a maximum depth of 15.5 feet, it is a shallow body of water. The shallow depth, coupled with significant nutrient and pollution in stormwater runoff, has had a significant impact on Como Lake water quality. In fact, CRWD began when a group of residents raised concerns about the water quality in Como Lake. Accordingly, the District has placed a high priority on improving Como Lake, as it is one of the most recognizable and well-loved water resources.


The Challenge

The biggest challenge facing Como Lake today is too much phosphorus, a pollutant carried to the lake through runoff in storm drains. Phosphorus comes from decaying organic matter like leaves, grass clippings, pet waste, and soil. Over time, high levels of phosphorus — three times higher than Minnesota standards — have led to algae blooms that choke the oxygen from the lake, leading to fish kills and strong odors mid-summer. CRWD and its partners have worked to reduce phosphorus flowing to the lake in stormwater runoff by 20% over the past two decades. Como Lake’s water quality remains poor due to the high levels of phosphorus that have built up in the lake over time. Excess phosphorous in the lake must be addressed to reach water quality goals.

"Capitol Region Watershed District is committed to improving Como Lake. Reducing phosphorus and controlling curly-leaf pondweed are critical for restoring balance." - Britta Belden, CRWD Water Resource Project Manager

The Solution

CRWD, with guidance and support from the City of Saint Paul, Ramsey County and the Minnesota Department of Natural Resources (DNR) have outlined the new Como Lake Water Management Plan implementing the industry’s best practices, science and technology. The Como Lake plan identifies strategies to address the water quality issues, which includes treatment of the water over the course of several years, beginning in the spring of 2020 with herbicide and alum treatments.

View Como Lake Management Plan

Spring 2020 Alum Treatment

Alum Treatment

  • Alum (aluminum sulfate) was applied to Como Lake this spring to reduce phosphorus being recycled inside of the lake.
  • The treatment is expected to dramatically reduce algae growth and improve water clarity and quality.
  • Alum is commonly used in drinking water treatment and has been a safe lake management tool for decades.

View Alum Treatment Factsheet

View Alum Treatment Updates blog post

Frequently Asked Questions