Aquatic invasive species (AIS) (sometimes called exotic, invasive, nonindigenous or non-native) are aquatic organisms that invade ecosystems beyond their natural, historic range. Their presence may harm native ecosystems or commercial, agricultural, or recreational activities dependent on these ecosystems. In fact, aquatic nuisance species can be spread many ways including ships, boats, barges, aquaculture, aquatic recreation (fishing, hunting, boating, diving, etc.), water gardening, seaplanes, connected waterways and many other pathways.

Below are a list of AIS that are currently affecting Forest Lake.


This invasive plant species grows  rapidly to form a dense mat- like structure at the surface that chokes out desirable native plant species and restricts  recreational  boating and swimming. CLP dies at the end of June/early July and floats to shore causing disposal problems. The decaying CLP releases   2-5 pounds of phosphorus/acre, thus supporting severe algae blooms and low water clarity.



This invasive species rapidly  propagates  taking over lakes, killing other mollusks, and attaching to boat motors/bottoms, docks, lifts and any hard surface in or near the water. Frequent removal of the ZMs is required to maintain equipment functionality. The razor sharp shells of dead ZMs  eventually  cover the bottom and  prevent swimming/wadding without adequate foot protection. Because the thin dead shells can be blown by wind and storms, they can  collect  in heaps and piles, which could block not only the  shallow channels  connecting our three lakes  but also  entrances to  bays/channels.


Flowering rush is a perennial plant that grows one to four feet high along shores in shallow, slow-moving water. In deeper water, it can grow in a submerged form that does not produce flowers. It flowers in early summer through mid-fall. Flowers comprise of three pink petals and three sepals arranged in clusters or umbels (umbrella shaped) on a flower stalk. Flowers typically bloom in June through early fall. Small buds that form in the clusters of flowers can disperse and grow into new plants. Flowering rush is difficult to identify when not in flower, as it closely resembles many native, beneficial shoreland plants in Minnesota, such as the common bulrush.


Untreated storm water runoff (yards, streets, storm sewers, ditches, culverts, etc) deposits 2100 lbs of phosphorus /year into Forest Lake. This is NOT fertilizer phosphorus. The phosphorus comes  from decayed grass/leaves/vegetation  and sediment. It can come miles from the lake and needs to be controlled by shoreline plants, rain gardens, settling ponds and  4-5 other techniques depending on the situation/location where it flows into the lake.  This phosphorus and phosphorus build up supports algae blooms/low water clarity. One pound of phosphorus can support 500 lbs of algae! This is why Forest Lake is categorized as “eutrophic” and rated as “impaired” in about half of our open water months.


Eurasian watermilfoil is a perennial plant that flowers twice a year, usually in mid-June and late-July. It can grow up to 20 feet tall, but typically only grows three to nine feet tall. It creates canopy-like structures as it grows toward the water’s surface. It primarily establishes through vegetative fragmentation—a fragment can break off, settle in the sediment, grow roots, and establish a new plant. The plant dies back in the fall, but the root system can survive the winter and begin growing again in the spring.



Purple loosestrife is a perennial plant found rooted in a range of wet soil habitats. It can grow in a couple feet of water or on dry shore near the water line. It is commonly found in roadside ditches. Plants range from two to six feet tall, with several half to one foot long flower stalks on a single plant. Plants bloom from early July to September, and then go to seed. Individual flowers have five or six pink-purple petals surrounding small, yellow centers. Single flowers make up flower spikes, which can be up to one foot tall. Flowers bloom from early July through September. It looks similar to many native, beneficial wetland plants found in Minnesota shoreland areas and wetlands

EMAIL   |​​     •    PHONE   |   612-751-4666    •    ADDRESS   |   P.O. Box 61 Forest Lake, MN 55025​