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Continued: Draining of Apple Valley lake yields limited benefit

  • Article by: LAURIE BLAKE , Star Tribune
  • Last update: July 19, 2014 - 6:36 PM

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.

 

Laurie Blake • 952-746-3287

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  • Curly-leaf pondweed can form in thick mats on a lake’s surface, complicating paddling and blocking light to other plants. When it dies, it promotes green algae.

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