Minnesota has nearly 150 species of aquatic plants, most of which are native species. Maybe you have encountered some of them while enjoying nearby lakes. To some, aquatic vegetation is a nuisance: plants that brush your legs while swimming or catch your fishing line sure don’t seem helpful at the time. But did you know that these same plants can actually help create conditions suitable for recreation? Although each person may view the plant kingdom with varying opinions, aquatic plants do play an important role in creating a healthy lake ecosystem.
Aquatic plants provide habitat for wildlife. Whether you fish or watch birds, you owe some gratitude to aquatic plants. These plants provide food (insects), shade, and cover – all of which are great for nesting and for young fish to grow. Waterfowl are also attracted to these areas, as they benefit from the abundance of fish and cover for themselves. Without areas of aquatic vegetation, many animal species would be unable to complete their life cycles.
Clear water is also served by aquatic vegetation. Research has shown that lakes can naturally sustain water clarity when at least 40% of the lake bottom grows vegetation (Canfield and Hoyer, 1992). In the PLSLWD, Lower Prior Lake is typically very clear and has 43% Plant Area Cover (PAC). Both Spring and Upper Prior Lakes, on the other hand, have poorer water clarity, and their PAC is 12% and 8%, respectively. Since Spring Lake has been treated with Alum in October of 2013, the water clarity has increased, and so has the vegetation.
Other benefits of aquatic plants include soil stabilization, absorption of undesirable nutrients, shade to keep the water cool, and beautification of the shoreline. All that being said, there is a difference between “good” and “bad” plants. Undesirable plants that should be removed include those not originally from this area (non-native), and those which out-compete native plants (invasive). Curlyleaf pondweed is one plant to watch out for that is both non-native and invasive.
Curlyleaf pondweed was introduced to the United States in the mid-1800s and is still a popular aquarium plant. These days it is found in many lakes throughout Minnesota, including Prior and Spring Lake. Curlyleaf pondweed harms ecosystems by outcompeting native plants and contributing to algal blooms as it decays. It blooms early in the season and will start to spread before most native plants can establish in the spring. Then it dies back during mid-summer, contributing nutrients to the water which algae use to grow.
All water users and the Watershed District play a role in managing non-native and invasive species like curlyleaf pondweed. The District surveys for curlyleaf pondweed every spring and treats when plants disrupt recreation, outcompetes native vegetation, and is further than 150 feet from shore. These treatments have proven successful on Spring Lake, eliminating the need for the District to treat curlyleaf pondweed from 2008 through 2015.
However, the District cannot manage invasive plants alone. Aquatic plants within 150 feet of shore are landowners’ responsibilities. When managing for invasive species, individuals must take care to remove them during an appropriate time of year and to leave native plants, as the invasive species grow readily in disturbed areas. For curlyleaf pondweed, treatment must be completed in the spring before the lake temperature surpasses 60°F. Treatment methods can include application of herbicides or physical removal of plants by pulling, raking, or cutting. Each treatment option will have its own positives and negatives, so it is useful to research each to determine what best meets your objectives.
If you had curlyleaf pondweed in excess this spring, chances are it will be back next spring, so you should start planning early. Knowing whether you plan to use a contractor or treat the invasive species yourself should be decided in advance. Remember that no matter how close to shore, aquatic plants growing in public waters are owned by the State, which enforces strict regulations on vegetation removal. Before attempting to control or remove any aquatic plants, contact your local Minnesota Department of Natural Resources office at (952) 496-4141. MN DNR staff can help identify plants, guide you through restrictions, and assist in identifying whether a permit will be required.
Aquatic plant management consists of balancing different needs. While many water users prefer lakes free of plants, they also desire recreational benefits which are only possible when plants are present in the ecosystem. Eradicating all aquatic plants is neither practical nor wise, but by taking informed action against problematic plant species, lake users can enjoy the lakes they desire and maintain a healthy ecosystem.
- To learn more about the DNR’s aquatic plant regulations and approved herbicides, visit its website at: http://www.dnr.state.mn.us/apm/index.html Here you can also find a list of vendors which offer treatment options such as hand or mechanical pulling, cutting, raking, or herbicide application. (PLSLWD does not endorse any of these vendors.)
- For assistance identifying non-native and invasive species in our lakes, visit the DNR’s Invasive Aquatic Plants page at: http://www.dnr.state.mn.us/invasives/aquaticplants/index.html
- To learn more about aquatic vegetation surveys within the District visit our Lake Monitoring page and skip to the “Aquatic Vegetation Surveys” or “Automated Vegetation Density Mapping (BioBase)” section.
Canfield DE Jr. Hoyer MV. 1992. Aquatic macrophytes and their relation to the limnology of Florida Lakes. Bureau of Aquatic Plant Management, Florida Department of Natural Resources, Tallahassee, Florida, 32303.