Another invasive plant takes root in Lake Minnetonka

Flowering rush, an invasive water plant, has taken root as the latest unwelcome species in Lake Minnetonka -- this time probably through the actions of a gardener, not a boater, the Department of Natural Resources says.

The DNR got word of the plant's presence in Lake Minnetonka on June 29. In searching 10 of the lake's 132 miles of shoreline so far, the DNR has confirmed its growth in Smith's Bay, Brown's Bay and Crystal Bay near Orono.

Because flowering rush has attractive pink flowers, giving it some appeal, and because it must be dug up with its roots to be transplanted, "we suspect the plant was purchased and planted in the lake or a pond nearby" by a water gardener, said Chip Welling, DNR's coordinator of aquatic invasive species management.

The plant is a nuisance because it can grow densely in 2 to 4 feet of water, like cattails, hindering entry to the lake from shore, Welling said.

The species has been spotted as the DNR has stepped up boat inspections to try to stop the spread of zebra mussels to the popular west metro lake. Zebra mussels were found this year in Prior Lake, the first infestation in a recreational lake in the metro area.

Because zebra mussels are spread most commonly by people hauling boats, boat lifts, water and other materials from an infested water body to a clean one, the DNR extended hours of inspections on boat ramps to Lake Minnetonka.

So far, Lake Minnetonka water samples show no evidence of the zebra mussels, the Lake Minnetonka (shoreline property owners) Association reported last week. The shell creatures can smother native claims, cling to boats and docks and foul beaches.

Flowering rush is the fourth invasive species to show up in the lake, following common carp, curly-leaf pond weed and Eurasian water-milfoil, Osgood said.

Each compromises lake water quality on its own and in combination with the others, he said.

The umbrella-shaped flowering rush plants were first found in Minnesota in 1968 and now grow in 21 lakes around the state, including Detroit Lakes, Welling said.

In an effort to eradicate them on Lake Minnetonka, the DNR plans to spray them within the next 10 days, Welling said.

It's against the law to buy or transplant flowering rush, and it has spread slowly by comparison to milfoil, which can take root and spread from a fragment of a leaf or stem carried accidentally from lake to lake on a boat, Welling said. Milfoil, first found here in 1987, has spread its dense green matts to more than 200 lakes around the state.

Laurie Blake • 612-673-1711