Because of the drought, the jury is still out on whether draining the lakes last winter reduced curly-leaf pondweed in two of the three Anderson Lakes in Eden Prairie.

"There is no water for the plants to grow in," said Kevin Bigalke, director of the Nine Mile Creek Watershed District. "The conclusion on success is probably not going to be until next spring. We aren't going to know that until the lakes have come back to full recovery."

At least the extended drought is eliminating a summer's worth of pondweed growth and seed production, he said.

In a widely watched experiment last winter with natural weed control, the watershed district drained most of the water from northwest and southwest Anderson Lakes, near Hwy. 169.

With the water gone, officials were counting on a dry, cold winter to freeze and kill the curly-leaf pondweed seed pods in the lake bed -- delivering cheaper, longer-lasting results than dousing the lakes with herbicides.

The harsh winter presented perfect conditions, Bigalke said. The cold and light snow supported the experiment, he said.

"January was miserable for us but it was great from the standpoint of freezing sediment.... We couldn't have had too much better conditions," he said.

Because the conditions were so favorable, there was no plan to drain the lakes for a second year -- "Although where conditions are at, we may get that naturally," Bigalke said.

Next Wednesday, the watershed district will review a University of Minnesota analysis of a limited number of lake bed samples taken before and after the draw down to determine the presence (or absence) of curly-leaf seed pods in the lake floor.

Curly-leaf pondweed -- is a native of Eurasia, Africa and Australia that may have come to the United States as an aquarium plant.

It has narrow, rippled leaves with jointed stems, floating leaves and greenish flowers, and it begins growing when lakes are still ice-covered.

The plant, which once covered 45 to 50 percent of the two Anderson lakes, has been growing in Minnesota for 100 years. Its growing cycle is out of sync with native plants.

Because it's the first plant up in the spring and the first to die in July, it leaves tangled vegetation on the water surface that blocks light to native plants. It typically decomposes in the heat of summer, adding phosphorous to the lake. Algae thrive on the phosphorous, turning the lake pea green.

Had spring and summer rains filled the lakes again as expected, it would have been clear by now if the pondweed had returned.

When the lakes come back, the district will look to see how much curly-leaf pondweed is there, check for improved diversity of native plants and measure for phosphorous, Bigalke said.

"If the average concentrations of phosphorus have been reduced, we can look at that as a success," he said.

Emptying lakes to control pondweed is new to the metro area and is considered only when lakes are shallow and easily drained. Bloomington's Mount Normandale Lake, west of Normandale Boulevard, is the next candidate in the Nine Mile Creek district.

Anderson Lakes homeowners are being patient with the drought and thinking of the draw-down experiment as a work in progress, said homeowners association president Mike Bendtsen.

With the lack of water, the lake bottom is mucky and difficult to get out on, he said.

"As for the weed from the homeowners point of view -- we haven't been able to get out on the lake to see it," he said.

Laurie Blake • 612-673-1711