Exotic Aquatic Plants

View PDF


What is an “exotic” species?

An exotic species is one that is found outside of its natural range. Exotic plant species that are currently a threat to Michigan lakes include Eurasian milfoil (Myriophyllum spicatum), starry stonewort (Nitellopsis obtusa), hydrilla (Hydrilla verticillata), and phragmites (Phragmites australis). Eurasian milfoil starry stonewort, and hydrilla are submersed species that grow underwater and phragmites is an emergent plant that grows along the water’s edge.


Why are many exotic plants a nuisance?

Outside their natural range, many exotic aquatic plants have no natural competitors or predators to help keep them in check. Exotic aquatic plants often have aggressive and invasive growth tendencies. They can quickly outcompete native plants and gain dominance.

Depending on the plant, dispersion can be by fragments, seeds, tubers or through over-wintering buds called turions. For example, Eurasian milfoil was first introduced to the United States in the 1940’s and spread rapidly by “vegetative propagation” whereby fragments of the plant break off, take root, and grow into new plants. Eurasian milfoil forms a thick canopy at the lake surface that can degrade fish habitat and seriously hinder recreational activity. Once introduced into a lake, Eurasian milfoil often out-competes and displaces more desirable plants. Starry stonewort, hydrilla, and phragmites also spread quickly and crowd out native plants.

What can be done to control exotic species?

Many exotic plants are transported on boats and boat trailers. If you trailer your boat from lake to lake, you should wash your boat and trailer before re-launching. With exotic species, an ounce of prevention is worth a pound of cure!


Early detection and rapid response is critical to preventing exotic species from getting a foothold and gaining dominance in a lake. Depending on the exotic plant, however, eradication may not be possible. Chances for control improve if your lake is monitored. Once an exotic plant infestation is detected, appropriate management options can be considered.