Lake Minnetonka WEATHER


Preventing and Managing Aquatic Invasive Species

Aquatic Invasive Species (AIS) are plants, animals and pathogens that are “out of place.” A species is regarded as invasive if it has been introduced by human action to a location, area, or region where it did not previously occur naturally (i.e., is not native), becomes capable of establishing a breeding population in the new location without further intervention by humans, and spreads widely throughout the new location.

Humans have created conditions where plants and animals can aggressively invade and dominate water bodies in three ways:


Introducing exotic species (from other regions or countries) who lack natural competitors and predators to keep them in check.


Disrupting the delicate balance of native ecosystems by changing environmental conditions (e.g., stream sedimentation, ditching, removing native plants) or by restricting or eliminating natural processes (e.g., fire). In such instances, even some native plants and animals can become invasive.


Spreading invasive species through various methods. Some examples:
  • Moving watercrafts from waterbody to waterbody without removing invasive plants and animals or draining water
  • Moving live fish from a waterbody
  • Releasing live non-native animals and plants into the wild
  • Carrying seeds of invasive plants on footwear or pet’s fur

AIS and Problematic Vegetation in Lake Minnetonka

Eurasian Watermilfoil

Eurasian Watermilfoil

Eurasian watermilfoil (EWM) was first discovered in Lake Minnetonka during the fall of 1987 in Excelsior Bay. Inspection of the lake the following year found that EWM was widespread throughout Lake Minnetonka. This indicated that EWM was introduced into Lake Minnetonka years before it was reported.

Eurasian watermilfoil (Myriophyllum spicatum) is a submersed invasive aquatic plant that was inadvertently introduced to Minnesota.  EWM can limit recreational activities on lakes by forming dense mats on the water surface, and alter aquatic ecosystems by displacing and out-competing native plants.

Until 2019 when the harvesting program was suspended, mechanical harvesting was used to maintain recreational access for the public and riparian property owners. Mechanical harvesting was the most cost-effective management option that the LMCD had to control EWM, CLP, and other floating vegetation lakewide. The top five to six feet of the plants were removed by the harvesters and this temporarily allowed for problem-free boating and swimming. In recent years, Curly-leaf pondweed (CLP) has also become a problem in the early season. The presence typically reduces in June. 

Aquatic Vegetation Harvesting

Coordinated Herbicide Treatments

Riparian lakeshore owners can manage EWM, CLP, and other invasive plants around their docks. For residents interested in chemical treatment or private mechanical harvesting, the MN DNR publishes the following lists of licensed Commercial Aquatic Pesticide Applicators and Licensed Mechanical Control Companies:

MN DNR Licensed Commercial Aquatic Pesticide Applicators

MN DNR Licensed Commercial Mechanical Control Companies

Zebra Mussels

Zebra Mussels

Zebra mussels were discovered in Lake Minnetonka by a local resident on July 27, 2010 and confirmed by MN DNR biologists on July 28, 2010.

The zebra mussel is a small, fingernail-sized mussel first found in Lake St. Clair near Detroit in 1988. This native of the Caspian Sea region in Asia is tolerant of a wide range of environmental conditions. To date, they have spread to parts of all the Great Lakes, the Mississippi River, and are showing up in inland lakes. A common problem they present is the clogging of water-intake systems of power plants, water treatment facilities, and the cooling systems of boat engines. Eventually, they may eliminate native mussel species. They also are safety hazards when in contact with feet and other body areas.

One factor in the rapid spread of zebra mussels is the reproductive rate of a female zebra mussel. Spawning generally occurs in the spring and can continue through the summer until fall. Over the course of a year, a female zebra mussel can produce up to one million eggs. These develop into microscopic, free-swimming larvae called veligers that begin to form shells. At about three weeks, they begin to firmly attach themselves to solid objects such as submerged rocks, dock pilings, boat hulls, and water intake pipes.

More information is learned through research projects, some conducted on Lake Minnetonka. More information is available through the following resources.


Blue-Green Algae

Blue-Green Algae

Blue-green algae are not algae at all, but rather types of bacteria called cyanobacteria. Cyanobacteria thrives when there is a combination of two factors: warm weather and nutrient-dense water. Some variations of cyanobacteria produce toxins and cause cause severe illness in humans and pets.

Can you prevent harmful blooms?
We cannot control the weather, but we can reduce the amount of nutrients introduced into the water through run-off. Learn more about Lake-Friendly Landscaping.


When in Doubt, Stay Out

Because you cannot tell by looking at blue-green algae whether it is toxic or not, it is best to avoid swimming or otherwise recreating in areas with algal blooms. If you or your pet are exposed to an algal bloom, be sure sure to rinse off with fresh water immediately.

For more information about possible health effects and the risk levels of different recreational activities, visit the MN Pollution Control Agency website.


Other Common Types of Algae

-Bryozoans- View MN DNR webpage

-Algal Blooms, Scums, and Mats in Ponds including Filamentous- View University of Arkansas