Enterprise Services raising Capitol Lake following draw-down to combat mudsnails

The Department of Enterprise Services (DES) is raising the water level in Capitol Lake following a draw-down that used the colder than normal temperatures to assist in the control of New Zealand mudsnails, a non-native snail that is classified as an invasive species.

Enterprise Services estimates it will take about two days for the lake to refill.

The lake was lowered between Thursday, Dec. 15 and Sunday, Dec. 18 to reduce the invasive mudsnail population in the lake. Mortality rates varied, depending on location. For example, sampling near Marathon Park showed a mortality rate of about 50 percent, while sampling along Powerhouse Road produced an estimated mortality rate of about 90 percent, according to the state Department of Fish and Wildlife, which monitors the mudsnail population.

Freezing does 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.

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 mudsnails have been found in fresh waters and estuaries, including at the mouth of the Columbia River. They can reproduce asexually, meaning just one mudsnail 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 mudsnails 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 series of five-mile radius surveys of area lakes and streams found that the mudsnails are spreading within Capitol Lake but have not invaded other nearby water bodies. The last survey was conducted in 2015.

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.

Drawdowns are conducted when weather conditions will be cold enough for the technique to be effective. A weeklong drawdown of the lake in December 2013 and another in February 2014 is estimated to have reduced the mudsnail population by 40 to 60 percent across all Capitol Lake including the middle and upper sub-basins, according to Fish and Wildlife. During this shorter duration freeze, Fish and Wildlife estimates the overall population reduction rate of the mudsnails at 20 to 40 percent.

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

Sign up to receive Capitol Lake updates via email or text message.

Sign up to receive Capitol Campus Updates via email or text message.

Follow Enterprise Services on Twitter.

Learn more about Visitor Services on Facebook.

Like Enterprise Services on Facebook.