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On Sunday, researchers collected dozens of the snails, each no bigger than a grain of rice, as a first step toward gauging the effectiveness of the saline rinse, expected to last through Friday.
They were collecting about 50 snails at each of several survey areas near Heritage Park, Marathon Park and midway up the basin. After the saltwater recedes, researchers can return to the survey areas identified by markers to collect the same number of snails to see how many died and to calculate the mortality rate.
Biologists aren’t expecting a complete die-off of the snails because salinity level in the water probably won’t climb high enough. That’s due to there being more freshwater in Capitol Lake than they would like before the saltwater is introduced.
An Olympia resident discovered the snail’s presence in Capitol Lake in October, the first such infestation in the Puget Sound region.
The species is troublesome because it outcompetes other species for food and, due to its small size, can be transported to other water bodies on the bottom of a boat, a dog’s paw or sole of a shoe.
Allen Pleus, aquatic nuisance species coordinator for the state Department of Fish and Wildlife, said a single snail can produce up to 230 offspring in one year.
“They clone themselves. They’re asexual,” he said. “They’re sort of like the perfect invasive species.”
The lake is expected to refill with freshwater by March 8, depending on the river flow.
The lake has been closed since late November to boating and other uses by humans, including walking on the shoreline or allowing dogs to wade in the lake. It will remain closed indefinitely, and a section of shoreline is cordoned off with yellow tape.
During a cold spell in December, the state drew down the lake to expose the snails to frigid temperatures in an effort to kill them off. Test plots showed a 98 percent mortality rate.
Christian Hill: 360-754-5427
chill@theolympian.com
