OLYMPIA - A cold, sunny day is a perfect time for people to bundle up and take a few laps around Olympia s Capitol Lake, but it s a terrible time to be a New Zealand mud snail.

The invasive snails that threaten a growing list of Washington State water bodies, cannot survive a hard freeze. And just to add to their misery, state agencies lowered the level of Capitol Lake to give the snails less protection from the bitter cold.

The technique worked with 90 percent efficiency in the past. But prolonged sub freezing spells are not an annual event in Western Washington, so the snails have rebounded since the last one in 2009.

Birds, fish and other animals show no interest in eating the snails, so they have been able to flourish. Biologists fear they could choke out native species and alter the eco system. So the bitter cold is a blessing, hostile weather is the snails only predator.

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