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

Enterprise Services, which manages the 260-acre lake, will begin lowering the water level at about noon. By Wednesday morning, most of the lake bottom will be exposed to the elements, although some pools and channel will still be covered with water. The drawdown will last several days, depending on weather conditions.

In December 2009, a five-day drawdown of the lake showed that freezing is an effective method for killing mudsnails: test plots showed that up to 98 percent of the snails died.

Freezing will not eliminate mudsnails from the lake. It is a control strategy for reducing the population. Once mudsnails are established in an aquatic environment, it is impossible to eradicate them without damaging other native species.

Since mudsnails have no natural parasites or predators in the Northwest, they multiply quickly, crowding out native species and threaten the long-term health of an infested water body. The snails can live in either fresh or brackish water and can reproduce asexually, meaning just one snail can introduce the species to a new area.

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 accidently introduced into another lake or river to begin another infestation.

A June 2013 survey of area lakes and streams found that the snails are spreading within Capitol Lake but have not invaded other nearby water bodies.

Mudsnails were first discovered in Capitol Lake in fall 2009. The lake is closed to boating and other uses until further notice because of the danger of spreading the destructive snails.

Enterprise Services coordinates mudsnail control strategies with the state's Invasive Species Council, departments of Ecology and Fish and Wildlife, the city of Olympia and others. The Department of Fish and Wildlife will conduct a limited survey and analysis of snail mortality rates during the drawdown.

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