The state began lowering the water level in Capitol Lake on Wednesday in a bid to freeze to death some of the New Zealand mudsnails that infest the lake.
The lake will remain drawn down as long as the cold spell stays in place. A similar draw-down of the lake in December 2009 triggered a 98 percent mortality rate in test plots over a five-day period.
Freezing isn’t expected to eliminate the snails, which multiply rapidly, are the size of a grain of rice and have no natural predators.
But the draw-down should help reduce the mudsnail population, according to the state Department of General Administration, which is working with the state’s Invasive Species Council, state departments of Ecology and Fish and Wildlife, City of Olympia, and others to combat the snail infestation first discovered in the lake in fall 2009.
The lake remains closed to boating and other uses until further notice because of the danger of spreading the snails, which can overwhelm lake habitat for native species and threaten the long-term health of an infested body of water.