Minnehaha Creek and connecting lakes in St. Louis Park and Minneapolis are also considered infested. The mussels eventually will damage water intake pipes and boats.
Zebra mussels are living in about half of Lake Minnetonka and have also been found at the upper end of Minnehaha Creek, according to a new survey by the Minnesota Department of Natural Resources.
The findings mean that the mussels are here to stay. Officials earlier held out the slim possibility that if the mussels were only in one or two places in the lake, they might be able to be isolated, and removed or killed. Now there is no way to keep them from moving down Minnehaha Creek into Minneapolis lakes.
Scientists found young mussels at 10 of 48 sites in an extensive search that began after a few mussels were first discovered in the lake on July 27.
"The widespread distribution of young zebra mussels in the eastern half of Lake Minnetonka indicates that there is a breeding population that has been in the lake for at least one year," said Luke Skinner, supervisor of DNR's invasive species unit.
Scientists found them also in Minnehaha Creek just below the dam at the outlet of Lake Minnetonka. Although they were not found farther downstream, DNR has designated the lake, Minnehaha Creek and several lakes connected to the creek as infested waters. The lakes include Meadowbrook in St. Louis Park, and Nokomis and Hiawatha in Minneapolis.
The designation allows additional regulations to prevent further spread of the fingernail-size mussels, such as washing and draining all water from boats and bait buckets when leaving infested waters.
The non-native mussels from central Europe have no natural enemies in North America, and their populations often explode a few years after they become established in new waters. At their earliest stage, they are microscopic and float freely in water. Later they attach to hard surfaces by the millions, damaging water intake pipes, boats and other equipment. The mussels also filter nutrients from the water, changing the ecology of lakes by starving native mussels and changing fish habitat. They interfere with swimming and other recreation after they die, when their razor-sharp shells accumulate on beaches.
The DNR surveyed the lake with scientists at the Minnehaha Creek Watershed District and the Lake Minnetonka Association. No zebra mussels were found in the western upper basin of Lake Minnetonka.
The mussels appeared in Minnesota in 1989 in Duluth harbor, and they since have spread to 17 inland lakes, including Mille Lacs, and to portions of the Mississippi, St. Croix and Zumbro rivers.
Tom Meersman • 612-673-7388
The DNR and watershed groups have scheduled two meetings to answer questions about the mussels:
AUG. 31, 7-9 p.m. Southshore Community Center in Shorewood.
• SEPT. 1, 7-9 p.m. Gillespie Center in Mound.
The agency has created a website for the Lake Minnetonka infestation: www.dnr.state.mn.us/minnetonka_zebra_mussels