Como Lake Aquatic Plant Management

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 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.

Como Lake Curly-Leaf Pondweed video from 2020.

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 in Como Lake in April 2020 and March 2021. 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 they do not produce turions and prevent future 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 Division and the Minnesota Department of Natural Resources, has been successfully reestablishing the native plant community by transplanting live plants in Como Lake since 2021.

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 negative impacts from carp in Como Lake have decreased. CRWD will continue to work on the removal of 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 impact water quality and clarity along with disrupting the native plant community. By reducing carp populations in Como Lake, we are working to ensure that conditions in the lake continue to improve.

The native aquatic plant community is closely monitored by CRWD and  Ramsey County Soil and Water Division and is rebounding in Como Lake thanks to ongoing transplanting efforts and curly-leaf pondweed control. In 2023, CRWD observed the highest plant diversity in Como Lake since consistent plant monitoring began in 2010. Twelve native species were observed, including three species that were not part of the transplanting efforts. The quantity of native plants observed also significantly increased. Plant abundance will hopefully continue to climb with future transplanting efforts and curly-leaf control.

In 2023, the curly-leaf pondweed population rebounded in the lake, signaling the need for management in 2024. In late March 2024, a low-toxicity herbicide called fluridone will be applied to the lake by a licensed applicator at a low-dose concentration of 2-4 parts per billion to target curly-leaf pondweed. The Minnesota Department of Natural Resources has issued a permit for this treatment.

The herbicide 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 that are already growing at the time of treatment, so the critically important native aquatic plants that start their growing season in late May will not be impacted. At low concentrations, fluridone has no contact restrictions and is safe for humans, pets, or wildlife. The water does not need to be avoided during treatment.