Aliens invading our lakes

Green aliens are invading our lakes! These aliens are not from a different planet, but from different continents, mainly Eurasia. This article will cover some common aquatic invasive plants, why they are harmful to our lakes, what the status is in this area and what you can do to protect our lakes.

I’ll start out by defining some commonly used terms. The terms “exotic”, “alien”, and “nonnative” can all be used to describe a species that does not naturally occur here, and has been brought here either accidentally or intentionally. In contrast, “native” plants occur naturally and are fully integrated into the ecosystem. Native aquatic plants are good and necessary habitats for fish, birds and other aquatic organisms.

Not all alien plants are harmful, but those that are can disrupt the natural ecosystem, out-compete native plants and take over large areas. These plants are considered “invasive” and “nuisance” species. Invasive aquatic plants can get out of control because there is nothing in the ecosystem naturally to keep the population in check. When invasive plants take over a lake or wetland, the biodiversity in the ecosystem can decrease, meaning that there are fewer different kinds of plants and animals that can live there. When invasive plants form dense mats, they change the habitat and make it unsuitable for fish, birds and other aquatic organisms.

The plants I’ll talk about today are Eurasian watermilfoil and Curly-leaf pondweed. For pictures, you can visit: With all these plants total elimination is probably not realistic, but lakes in the area keep the populations in check by spraying herbicides. To spray these plants, a DNR permit is required. The DNR has grants available for lakes to obtain funding for control of these plants, for more information visit: It is very expensive to control these plants with herbicides, so the best thing to do is to prevent them from entering the lake in the first place.

Eurasian watermilfoil is probably the plant you hear most about. It is present in some lakes in Cass and Crow Wing Counties, so we need to be vigilant. In Crow Wing County, the lakes that have been confirmed to have Eurasian watermilfoil are: Bay Lake, Ossawinnamakee Lake, Ripple River between Bay Lake and Tame Fish Lake, and Ruth Lake. In Cass County, Eurasian watermilfoil has been found in Leech Lake. Any lakes that have high summer boat traffic and tourists from metro lakes are very vulnerable to Eurasian watermilfoil infestation. Once it is established, it grows in such dense mats that it is tough to swim and boat through. If you’ve ever been on Lake Minnetonka, you’ll know what I mean. To prevent its spread make sure you check over your boat, trailer and propeller every time you put your boat in and take it out of the water. Eurasian watermilfoil can spread by a single segment of stem and leaves. There is a closely related native plant called northern watermilfoil. Northern watermilfoil has 5-6 leaflets per plant while Eurasian watermilfoil has 12-21 leaflets per plant. If you think you have found Eurasian watermilfoil, save a sample of it and report it to the DNR (1-888-MINNDNR).

Curly-leaf pondweed is a nuisance because it can form dense mats in early spring that interfere with recreation. When it dies off in June, it washes up in thick piles on the shoreline. It has wavy leaves with serrated edges and a flat, reddish stem. Like Eurasian watermilfoil, it can spread from remnants of the plant left on boats. Curly-leaf pondweed grows best in fine, silty sediment and can be controlled with chemicals. Curly-leaf pondweed can be confused with whitestem pondweed, which has a more round green stem.

Please be vigilant in the spread of aquatic invasive plants. Keep recreation on our lakes enjoyable and the lake ecosystem healthy. At boat landings, there are usually DNR signs telling which invasive species are present in the waterbody and how to prevent their spread. Never transplant aquatic plants that you haven’t bought at a nursery and are unsure of what they are. For more information and pictures of these plants, visit:


  1. Rick Bowman says:

    Is there a way to test for any invasive species, or is it just by site.