Results inconclusive on effort to freeze out invasive snail

OLYMPIA - A test to see whether drawing down Capitol Lake in below-freezing weather would kill a pesky aquatic invader was inconclusive Thursday, according to a state Department of Fish and Wildlife biologist.

Biologists found some frozen New Zealand mudsnails and others that may or may not have died from exposure to the frigid overnight temperatures, said Allen Pleus, an aquatic invasive species coordinator for Fish and Wildlife.

A layer of ice that has formed over the lake sediments where the tiny snails reside served as a blanket of insulation, protecting some of the snails.

“We’re still interested in future draw-downs of the lake,” Pleus said. “It’s probably the most effective tool with the least amount of consequences on other species.”

He said the goal would be to draw the lake down ahead of a cold spell so ice doesn’t have a chance to form before the temperature-sensitive snails are exposed to the weather.

Left unchecked, the lake invader that was discovered last month could blanket the lake bottom, disrupting the lower end of the food chain.

It’s already present in the north basin at concentrations as high as tens of thousands per square meter of surface.

The state Department of General Administration, which manages the 260-acre manmade lake, closed the lake to public use Nov. 25 to keep the snail from spreading to other water bodies. The Capitol Lake infestation is the first in Western Washington.

The snail, introduced to the United States in the 1980s, has spread across the West, including the lower Columbia River and Long Beach Peninsula freshwater canals.

John Dodge: 360-754-5444