About Como Lake
Como Lake in Saint Paul, Minnesota, is a small urban shallow lake that is fed by stormwater runoff from the surrounding 1,711-acre watershed. When it rains or snow melts, water flows over rooftops and paved surfaces into storm drains, picking up pollutants like phosphorus, trash, chloride and dirt along the way and carrying them to the lake.
Capitol Region Watershed District (CRWD) has been working to improve Como Lake’s water quality for nearly three decades to support ecosystem health, enhance recreational opportunities, and increase the lake’s resilience. In recent years, Como Lake’s water quality has improved through ongoing strong community support and strategic management activities led by CRWD, the City of Saint Paul, and partners.
Water Quality Monitoring
Como Lake is sampled twice a month from April to October by Ramsey County Public Works to monitor water quality parameters, including temperature, oxygen, water clarity, nutrients (like phosphorus), chloride, and bacteria.
CRWD also operates three monitoring stations in Como Lake during the open water season that continuously measure dissolved oxygen, pH, temperature, and conductivity near the lake bottom. CRWD staff download the monitoring station data weekly and take a Secchi Depth reading of water clarity.
How is Como Lake’s Water Quality?
The dials show the results from the most recent water quality samples taken from Como Lake and how they rank in our lake grading system. The individual grades for each parameter are combined to calculate the current lake grade (as of the date shown). Sample results and lake grades are updated every two weeks from April to October. Explanations of the grading system and parameters are below in “Determining Water Quality.”
Determining Water Quality
Grading System and Impaired Waters
We use Como Lake’s monitoring data to determine the lake’s water quality status using a letter (A-F) grading system. The letter grade is based upon averages for Total Phosphorus (TP), Chlorophyll-a (Chl-a), and water clarity measured by Secchi disk (Secchi depth).
A body of water is considered “impaired” if it fails to meet one or more State water quality standards. The Minnesota Pollution Control Agency (MPCA) established numeric water quality standards for deep and shallow lakes using three water quality parameters (TP, Chl-a, and Secchi Depth) to assess water quality and classify and compare Minnesota lakes. Como Lake is currently listed on the MPCA’s impaired waters list for mercury in fish tissue, nutrients, and chloride impairments.
Phosphorus
One of the primary issues facing Como Lake today is too much phosphorus, a nutrient carried to the lake through stormwater runoff.
Phosphorus is a common element and critical for plant growth, but too much phosphorus in water can harm aquatic life, reduce water clarity, and lead to toxic algae blooms. Phosphorus in Como Lake 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. The invasive aquatic plant Curly-Leaf Pondweed (CLP) also adds phosphorus to the water when it dies off and decays summer.
Chlorophyll-a
Chlorophyll-a is the main pigment found in algae, and its concentration indicates the amount of algae in the water. Elevated levels often reflect nutrient pollution and decreased water clarity.
Secchi Depth
Secchi Depth measures water clarity. A larger depth means clearer water. It’s an indirect indicator of algal levels, suspended solids, and overall lake health
The Secchi Depth is determined using a Secchi disc, a black and white disc lowered into the water until it’s no longer visible. The deeper you can see the Secchi disc in the water, the better the water clarity, the more light can penetrate and help native plants to grow.
Lake Grade Over Time
We determine the annual average Overall Lake Grade by calculating the individual annual average (May-September) grade for each parameter (TP, Chl-a, and Secchi Depth) and then combining the annual averages to calculate the Overall grade.
Annual average Lake Grades in Como Lake have fluctuated over time, but have generally remained below a B with an average grade of C-. Since 2020, improvements in the lake’s water quality have resulted in higher annual average Overall Lake Grades in the C range, up from the D range. Lake grades for all of the District’s lakes are included in our annual Lakes Data Summary Reports, available on the Monitoring Program page.
Efforts to Improve Como Lake
CRWD is committed to improving water quality in Como Lake. In 2019, CRWD created a revised Como Lake Management Plan that included input from residents and community partners. The plan builds on the past two decades of work around the lake with a specific focus on management within the lake.
Since beginning in 1998, CRWD has completed over 75 projects to reduce phosphorous flowing into Como Lake from the surrounding neighborhoods. From neighborhood leaf clean-ups to residential curb-cut rain gardens to large projects like Como Golf Course stormwater improvements, they all add up to reducing pollution flowing into Como Lake.
You can help protect your local lakes, rivers and wetlands by taking the simple actions on our Act Now page.