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Runners stayed close to Lake Nokomis to stay cool this summer. Last fall’s $73,000 weir upgrade is working to fight zebra mussels, which clog water intakes and cut people’s feet and fishing lines.

ELIZABETH FLORES • eflores@startribune.com,

Lake Nokomis gets added muscle against invasives

  • Article by: Bill McAuliffe
  • Star Tribune
  • August 18, 2013 - 9:25 PM

 

A remodeled weir between Lake Nokomis and Minnehaha Creek got its first workout last week, likely keeping zebra mussel embryos in the creek but letting water out of the lake.

The weir received a $73,000 upgrade last fall from the Minnehaha Creek Watershed District (MCWD) in response to the 2010 discovery of zebra mussels in Lake Minnetonka, which feeds Minnehaha Creek. Zebra mussel embryos have been detected in the creek, but not in city lakes, two of which — Harriet and Nokomis — have short outlets into the creek.

The rapidly reproducing invasive aquatic pest can form clusters on dock supports, smother native mussels and clog water intakes, while its sharp shells can cut people’s feet and fishing lines.

The remodel strengthens the weir by replacing an inflatable base that was installed in 2000 with a permanent but adjustable system of metal “logs,” which can be removed to let water out of the lake and into the creek. But that will be done only rarely, noted Rachel Crabb, water quality supervisor for the Minneapolis Park and Recreation Board, which will operate the weir. That’s because several conditions have to align.

The weir will be lowered when the lake level is above its “ordinary high water level” — a designated shoreline level — and also more than a foot above the creek level, Crabb noted. When that difference is achieved and the MCWD agrees not to increase the flow of water out of Lake Minnetonka into the creek — and there is no rain in the forecast for 48 hours — officials can lower the weir.

Due to heavy rains in spring and early summer, both the creek and the lake had been high.

Crabb said parks officials had wanted to let water out of the lake earlier this season, but the creek had been too high. The creek dropped enough in recent days for the weir to be opened Tuesday and closed Thursday. The flow out of Lake Minnetonka into the creek Friday was at its lowest rate since June 21.

Last week’s operation will likely be the only one this season, Crabb said.

As a result of the opening, Lake Nokomis’ surface dropped 4 inches.

Parks workers will continue to test the lake for evidence of zebra mussels, said park district spokeswoman Robin Smothers.

 

Bill McAuliffe • 612-673-7646

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