Exotic and Invasive Plant Species

A problem facing some District Lakes is the growing abundance of nuisance exotic species, especially  Flowering Rush, and Curly Leafed Pondweed.  As noted elsewhere, these plants replace native species, alter shoreline sedimentation patterns, interfere with boating, swimming and fishing, cause shoreline damage, and hardship to shoreline residents.

Flowering Rush was probably introduced by accident in the mid-1970’s in Dead Shot Bay (Curfman Lake). From there it has spread throughout Big and Little Detroit,  down the Pelican River into Muskrat, and now into Sallie and Melissa.  Flowering Rush,   declared an “Undesirable Exotic Species” by the State of Minnesota in 1993, is found in only a few other places in the state.  It has a very aggressive root system,  and apparently spreads by the accidental transplant of root-fragments.  For almost 15 years the District has tried to manage this problem by repeated harvesting without much success.  In 2003 a herbicide testing program was begun.  (See Chemical Treatment - Flowering Rush.)                 IMAGE

Curly-Leafed Pondweed is found in many lakes in Minnesota,  and is widespread in District Lakes, including Big and Little Detroit,  Muskrat, Sallie and Melissa and is well-established in the Pelican River between these lakes. An annual plant with an unusual growth habit,  it germinates from seed in the fall, grows under the ice in the winter,  and matures in May or June. When it dies the plants break off from their stem, float to the surface, form large mats, and eventually reach shore, causing great hardship to shoreline residents, boaters and fishermen. In extreme cases,  the decaying weed masses can deplete oxygen and cause the deaths of many small fish.         IMAGE

Purple Loosestrife is found in some wetlands lying near Detroit Lakes. It is known to displace native species. The District has no program to control this exotic, the DNR does use some biological controls (beetles) to curtail infestations.