The state Department of Enterprise Services began lowering the water level in Capitol Lake on Thursday to fight the New Zealand mud snails that have invaded the lake.
The goal is to expose the tiny mollusks to the cold weather and reduce their population. The department expects that most of the lake’s bottom will be exposed to the elements Friday through Sunday, when temperatures are forecast to dip into the low 20s at night and hover just above freezing during the days.
The 260-acre lake will need two days to fill back up.
These rapidly-reproducing freshwater mollusks are about as long as a grain of rice and wreak havoc on the local food chain by outcompeting native aquatic snails and insects. They have no known predators or parasites in Washington.
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The species was first discovered in Capitol Lake in 2009. The lake has been closed to boating and other recreational uses since to prevent spreading the mud snails.
The state Department of Fish and Wildlife monitors the mud snail population. Similar lake drainings in 2013 and 2014 helped eliminate between 40 and 60 percent of the mud snails in the lake, the state estimates.