The Department of Enterprise Services (DES) will begin drawing down the water level in Capitol Lake today, Thursday, Dec. 15, to use the colder than normal temperatures to assist in the control of New Zealand mudsnails, a non-native snail.

Most of the lake bottom will be exposed to the elements by Thursday evening, although some pools and channels will still be covered with water. The drawdown will last until Sunday, Dec. 18. Enterprise Services estimates it will take about two days for the lake to refill.

Freezing will not eliminate mudsnails from Capitol 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 harming native species.

A weeklong drawdown of the lake in December 2013 and another in February 2014 is estimated to have killed 40 to 60 percent of the snails, according to the state Department of Fish and Wildlife, which monitors the mudsnail population.

Mudsnail mortality rates will vary depending on how low the lake can be lowered, how fast it refills and how deep the freezing level penetrates the exposed lakebed.

Enterprise Services, which manages the 260-acre lake as part of the Capitol Campus, coordinates mudsnail control strategies with the state's Invasive Species Council, departments of Ecology and Fish and Wildlife, the city of Olympia and others.

New Zealand mudsnails have no natural parasites or predators in the Northwest. They reproduce quickly, crowding out native species and disrupting the food chain. The snails have been found in fresh waters and estuaries, including at the mouth of the Columbia River. They 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 accidentally 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 risk of spreading the snails.

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