When Apple Valley decided to drain Long Lake last winter in an attempt to revive its water quality and fight an invasion of curly-leaf pondweed, the key question was: Would the weather cooperate?

Boy, did it ever.

One of the coldest winters on record gave the pondweed turions (a version of roots) buried in the lake bed the desired hard, killing freeze.

The result?

The lake is not cleared of pondweed but the concentration is reduced, said Jeff Kehrer, natural resources director for Apple Valley.

The weed is still growing in the lake in similar locations as in the past “but in much lighter levels,’’ Kehrer said.

He considers the drawdown a success. But many residents say it did not deliver the improvement in water quality they were hoping for.

“I do think the clarity of the water was improved, especially in the early spring.” said Paul Habegger, president of the Long Lake Watershed Association. “And I do think that the curly-leaf pondweed came up later than it usually does. We were giddy for a while, thinking that this thing really worked.

“But it came back and came back with a vengeance.’’

The pondweed may have been knocked back. But that brought light into the lake that allowed other weeds to grow, Habegger said.

“Is the overall aesthetic and quality of the lake better? I think most people would say no. I think the weather conditions [for the drawdown] were perfect, and if we didn’t hit a home run now, that proves it’s not a panacea.’’

The lake is choked with so much algae and other weeds that a paddleboat can’t cut through it, said Greg Johnson who has lived on Long Lake for 10 years.

“I propose that we chemically knock it out,’’ Johnson said.

A lot of people on the lake do want to use chemicals, but that may not be as simple as it sounds, Habegger said. Permits would be needed from the state. And residents ringing the lake would face some cost.

The next step is to come up with a new five-year plan and chemicals may figure into that, Habegger said.

Kehrer said testing of the lake water will continue over the summer and a plant survey in the fall will determine if wanted native plants benefited from the draining.

One lake to another

Apple Valley drained the 37-acre Long Lake in September. The water was piped under Pilot Knob Road into adjoining Farquar Lake.

The goal was to expose Long Lake’s bottom to a hard winter freeze that would kill the curly-leaf pondweed that has been fouling the water.

Draining lakes for the fall and winter and allowing them to fill up again in the spring is the most dramatic tool in Minnesota’s campaign to restore water clarity and bring back native aquatic plants.

The Department of Natural Resources regularly draws down lakes in outstate Minnesota to keep them hospitable for waterfowl. But in the metro area the practice is rare.

To drain the water from Long Lake, a $130,000 drain was installed in 2009 to make it possible to lower the water level every four years or so to control the pondweed, Kehrer said.

Pondweed is a problem because it forms thick mats on the surface through June and July, making it difficult to canoe and kayak.

Because it is the first plant to come up in the spring, curly-leaf blocks light to more slowly growing native plants. When it dies back at the end of July, it releases phosphorus, which promotes green algae.

Herbicides and mechanical harvesting are often used. But the weed is now so common on metro lakes that the state Department of Natural Resources has said that eradicating it is not a realistic goal.