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The water level at Capitol Lake will be lowered this week in an effort to control New Zealand mudsnails, an invasive species. The current cold-weather conditions provide an opportunity to kill snails by freezing them.

A draw-down of the lake in December 2009 showed that freezing is an effective method for killing mudsnails: test plots showed up to a 98 percent mortality rate over a five-day period.

The Department of General Administration, which manages the 260-acre lake, began lowering the water level around 1 p.m. on February 23. The lake will remain drawn down for several days, depending on weather conditions. No survey work or other mudsnail control testing will be done by the state during this draw-down.

Freezing is not expected to eliminate mudsnails from the lake. It is a control strategy for reducing the population. Mudsnails multiply quickly, can crowd out native species and threaten the long-term health of an infested body of water. They have no natural parasites or predators in the Northwest.

Because of their small size – about the size of a grain of rice when fully grown – the snails can be easily transported on the bottom of a boot or a dog’s foot pad and then accidentally introduced into another lake or river to begin another infestation.

The lake remains closed to boating and other uses until further notice because of the danger of spreading the destructive snails. They can live in either fresh or brackish water and can reproduce asexually, meaning that just one snail can introduce the species to a new area.

General Administration is working in coordination with the state’s Invasive Species Council, departments of Ecology and Fish and Wildlife, the City of Olympia and others to develop further snail control strategies.

• More on mudsnails: http://wdfw.wa.gov/ais/species.php?Name=potamopyrgus_antipodarum

For more information
Jim Erskine, GA Communications Office
(360) 902-7206, jim.erskine@ga.wa.gov

GA on the web: www.ga.wa.gov