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Como Lake Aquatic Plant Management

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.

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 and its aquatic plant community. 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 in CRWD.

The Challenge

Curly-leaf Pondweed

An invasive aquatic plant known as curly-leaf pondweed is causing problems in Como Lake. In early summer, curly-leaf pondweed is able to spread plant buds called “turions.” Each plant produces up to 100 turions that fall off and settle to the lake bottom to grow new plants. Over the winter the new plants begin growing under the ice, allowing them to outcompete native plants that begin their growing season in May.

Curly-leaf pondweed was first observed in Como in the early 1990s and was possibly introduced by boats, boot treads, or aquarium plants.  Curly-leaf pondweed thrives in murky water. The conditions in Como Lake are just right for curly-leaf to be highly successful and out-compete native species. Prior to herbicide treatments in 2020 and 2021, it had come to dominate 90% of the plant community in the lake. Visitors to Como Lake might notice a strong odor in the summer as all the curly-leaf pondweed dies off for the season and decomposes in the water. Controlling curly-leaf pondweed is a critical step for restoring balance in Como Lake’s ecosystem.

Common Carp

Common carp are another concern for the native aquatic plant community in Como Lake. Common carp are invasive fish that contribute to poor water quality by stirring up the lake bottom while searching for food. During feeding, they uproot plants, muddy the waters for native fish, and allow excess nutrients stored in the lake bottom to be released and later consumed by algae. Common carp are one of the most damaging aquatic invasive species due to their wide distribution and severe impacts in shallow lakes and wetlands. CRWD has conducted surveys of common carp in Como Lake and found their population to be above the critical threshold for water quality.

Eurasian Watermilfoil

Invasive Eurasian watermilfoil was first identified in Como Lake in the summer of 2024. The Minnesota Department of Natural Resources (DNR) investigated the report of the invasive aquatic plant and then formally listed Como Lake as infested with Eurasian watermilfoil. The DNR posted an orange invasive species alert sign by the boat launch to notify the public of its presence in Como Lake.

Eurasian watermilfoil can grow and spread rapidly, forming a dense canopy on the water surface that prevents light from reaching native aquatic plants below and interferes with recreational boating. CRWD is working to keep Eurasian watermilfoil from spreading in Como Lake and reduce its presence alongside curly-leaf pondweed control.

Como Lake Curly-Leaf Pondweed

Como Lake Curly-Leaf Pondweed video from 2020.

The Solution

In 2019, CRWD, with guidance and support from the City of Saint Paul, Ramsey County, and the Minnesota Department of Natural Resources, outlined the Como Lake Management Plan. By implementing the industry’s best practices, science, and technology, the Como Lake Management Plan identifies strategies to address water quality and ecosystem health issues, including those caused by the presence of invasive curly-leaf pondweed.

To begin addressing the curly-leaf pondweed problem and to support other ongoing water quality improvement projects, CRWD implemented two whole-lake herbicide treatments of fluridone in Como Lake in April 2020 and March 2021. Fluridone limits a plant’s ability to photosynthesize, so curly-leaf pondweed cannot grow bigger and produce plant buds (called “turions”) that further the plant’s spread in Como Lake. Fluridone only affects plants already growing at the time of treatment, so it does not impact the critically important native aquatic plants that start their growing season in late May. At low concentrations like the applications in Como Lake, fluridone has no contact restrictions and is safe for humans, pets, or wildlife. The water does not need to be avoided during treatment.

Following these treatments, plant surveys showed that curly-leaf pondweed decreased by 96% from pre-treatment levels—a major success in managing this aggressive invasive. However, once curly-leaf pondweed is in a lake system, it will never fully go away and needs to be regularly managed to keep the population under control. It is especially important to treat curly-leaf pondweed early in the season so it does not produce turions and spread.

Native aquatic plants are critical to Como Lake’s water quality and ecosystem health and provide food and shelter for wildlife such as ducks, turtles, fish, and bugs. To enhance and support the native aquatic plant community in Como Lake following the herbicide treatments, CRWD, with assistance from Ramsey County Soil and Water Conservation Division and the Minnesota Department of Natural Resources, is reestablishing the native plant community. Since 2021, a combination of strategies has been used, including transplanting live submergent plants, planting seeds harvested from plants currently growing along the shoreline, and planting nursery-grown emergent plants. The native plant population is improving as a result of these activities. CRWD and its partners will continue to monitor our efforts to revitalize the lake’s native plant community.

To support further establishment and growth of native aquatic plants, CRWD has been working to reduce carp populations in Como Lake through netting and electrofishing since 2022. Through these efforts, carp populations are now below the critical threshold for water quality, and the carp’s negative impacts on Como Lake have decreased. CRWD continues to work on removing common carp in Como Lake since they uproot plants and severely disturb the upper layer of the lake bottom when feeding. Even small populations of carp in the lake can degrade water quality and clarity, and disrupt the native plant community. By reducing carp populations in Como Lake, we are working to ensure that conditions in the lake continue to improve.

Results and Ongoing Efforts

In 2023, the curly-leaf pondweed population unfortunately rebounded in Como Lake. We recognize that controlling the curly-leaf pondweed population will be essential to restoring the native plant community in the lake. Therefore, we created a five-year treatment approach to reduce the sprouting period of viable turions. We applied the herbicide fluridone in the early spring of 2024 and 2025, which were the first two years of this treatment approach.

The spring 2026 treatment will use a new herbicide called Galleon. Galleon targets an enzyme in the plant that is required for amino acid production. Since amino acids are key building blocks needed for plant growth, the plants will stop growing and eventually die after exposure to Galleon.  This treatment will occur in Como Lake this spring, shortly after ice-off, when curly-leaf pondweed is growing in abundance, and native plants have not yet started growing.  A licensed applicator will apply it at a low-dose concentration of 6 parts per billion. The Minnesota Department of Natural Resources issued a permit for this treatment. Like fluridone, Galleon has no contact restrictions or safety concerns for humans, pets, or wildlife, and the water does not need to be avoided.

Stay tuned for more information regarding future herbicide treatments to reduce both curly-leaf pondweed and Eurasian watermilfoil.

A long, thin stem of curly-leaf pondweed with many curly leaves is held out on someone's palm.
An invasive aquatic plant known as curly-leaf pondweed is causing problems in Como Lake.
Person in waders is holding up a large, tangled clump of curly-leaf pondweed while standing in a lake.
Large mats of curly-leaf pondweed were common in Como Lake before herbicide treatments.
A flat, face up palm holds three, small plant buds with curly green leaves that are shaped like pinecones.
Curly-leaf pondweed reproduces by plant buds called turions that resemble small pinecones. Each plant produces up to 100 turions each year.
A shallow lake bed covered in curly-leaf pondweed just below the surface of the water.
Curly-leaf pondweed grows during the winter and is already close to the surface of the lake by ice out in early spring.
A person standing in a motorized boat with two large containers in it on a lake. There is snow covering the far lakeshore and the trees don’t have leaves on them.
CRWD implemented whole-lake herbicide treatments in Como Lake in the early spring of 2020, 2021, 2024 and 2025 to target curly-leaf pondweed.
A smiling person stands in a boat holding a common carp. The fish over 24 inches in length with large, brownish-green scales and a pair of long, whisker-like barbels under its mouth.
Common carp stir up the lake bottom when feeding which uproots plants and muddies the water.
Two smiling women are sitting in a boat on a lake are wearing life vests and holding up clumps of aquatic plants from large plastic bins filled with native plants.
CRWD transplants native aquatic plants in Como Lake to support the reestablishment of the lake's native plant community.
A canoe paddle extends into a lake with submerged aquatic plants crowding the lake surface.
Invasive Eurasian watermilfoil was first identified in Como Lake in the summer of 2024.
A person standing in a lake near the shoreline, surrounded by tall green reeds with a green canoe nearby. They are wearing waders and a red life vest.
CRWD staff harvested seeds from native plants in Como Lake.