CRWD's COVID-19 Response 

Herbicide Treatment Update

Capitol Region Watershed District (CRWD) is committed to improving water quality in Como Lake, a beloved water resource in Saint Paul. 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 Como Lake plan identifies strategies to address the water quality issues, which includes treatment of the water over the course of several years, beginning this spring.

Learn more about the Herbicide and Alum Treatments

Change is coming to Como Lake

This spring two treatments to address water quality will occur, an herbicide treatment and an alum treatment. The first is an application of the herbicide Fluridone to combat an invasive aquatic plant called curly-leaf pondweed. It was first observed in the early-1990s and has come to dominate 90% of the plant community in the lake. It was likely introduced by a boat, boot treads, or aquarium plants. Curly-leaf pondweed thrives in murky water. The conditions in Como Lake are just right to allow for the plant to be highly successful and out-compete native species. Controlling curly-leaf pondweed is critical for restoring balance in Como Lake.


On Monday, April 13, the herbicide Fluridone will be applied by a licensed contractor to the whole lake at a low concentration of 4 parts per billion and will be maintained for 60 days. It will be applied from a boat over the course of one day. Additional applications may be necessary during the 60 day period to maintain the concentration level.

On Tuesday, May 5, a bump treatment of the herbicide Fluridone was applied to Como Lake to ensure the correct concentration is maintained for the full 60 day period following the initial application.

There are no contact restrictions with Fluridone, so visitors, pets, and wildlife do not need to avoid the water during the application. Monitoring will occur throughout the treatment and the months following to maintain safe concentrations and to determine its effectiveness.

In June and July there will be a noticeable reduction in both plant mass and well, smell. At the height of summer, visitors to Como Lake often notice a strong odor as all the curly-leaf pondweed dies off for the season and decomposes in the water. After the Fluridone treatment this year the degree of die off should be greatly reduced.

In summer curly-leaf pondweed is able to spread with seeds called “turions.” Each plant produces up to 100 turions that fall off and settle to the lake bottom to form new plants. Over the winter the new plants begin growing under the ice, allowing them to out compete native plants. It’s anticipated that there will be fewer turions this year since the plants will not reach maturity following the herbicide treatment. CRWD will continue to monitor the plant community in Como Lake to measure the success of Fluridone treatments and the return of native plants.

Fluridone to control curly-leaf pondweed

Fluridone is an herbicide that stops plants from making chlorophyll so they are unable to photosynthesize. Plants will die within about 2 months of treatment as they are unable to make food. Fluridone is only effective for plants that are growing at the time of treatment. With application in early April the herbicide will target curly-leaf pondweed since native aquatic plants haven’t started their growing season.