Play Live Radio
Next Up:
0:00 0:00
Available On Air Stations

State Officials Seize Cold Snap, Freeze Out Invasive Snails In Capitol Lake

A cold snap might be an effective tool for fish and wildlife managers trying to stop the spread of a tiny invasive species. Capitol Lake in Olympia is serving as a testing ground for freezing out New Zealand mud snails. 

Tiny, Fast-Spreading Creatures

Credit Allen Pleus / Washington State Department of Fish and Wlidlife
Washington State Department of Fish and Wlidlife
Jesse Schultz, the lead aquatic invasive species biologist for the state Department of Fish and Wildlife.

The snails first appeared in the Columbia River in 2002. Then an Olympia resident on a bird-watching trip first found them in Capitol Lake four years ago. 

The creatures are about the size of a grain of rice. Though tiny, they outcompete native insects that serve as food for endangered fish and other aquatic life. And because they reproduce asexually, it takes just one snail to introduce the species to a new area.

No one knows for sure how they first got here, but once they start multiplying, they’re so small they can easily hitch a ride on just about anything, from a muddy boot or kayak paddle to the shovels and equipment used by landscape restoration crews.

Nowadays, New Zealand mud snails are all over the western states and spreading fast.

“Until 2009 they were only known to be in the lower Columbia River. And then we found them in 2009 in Capitol Lake,” said Allen Pleus, the aquatic invasive species coordinator for the Washington State Department of Fish and Wildlife.

Seizing The Cold Snap

Pleus said experts looked to Scandinavia for a non-toxic method to exterminate the snails. And Olympia’s man-made lake provides a closed system where they can test the technique of freezing them out.

When the temperature drops to below freezing, they drain the lake so the lake bed ices over. Earlier this month, the five-day cold snap provided just the right scenario, said Pleus: "Dry enough, cold enough and long enough."

Credit Washington State Department of Fish and Wlidlife
Washington State Department of Fish and Wlidlife

They monitored five sampling sites where they scooped up icy mud and debris with snails in it. On day one, Pleus says 15 percent of the snails were dead from exposure.

“And then after the fifth day, we went out and collected in those same areas and 100 percent of the snails were dead,” Pleus said.

They're not gone from the lake, Pleus says, because they burrow into the mud and only the top layer of ice that's exposed is cold enough to kill them all. But it's a start.

The hope is that this technique could eventually be used in other areas to slow their spread. But the simplest method is just to take along a stiff-bristled brush and sweep off anything that might be carrying the snails or seeds of other invasive species.  

Bellamy Pailthorp covers the environment for KNKX with an emphasis on climate justice, human health and food sovereignty. She enjoys reporting about how we will power our future while maintaining healthy cultures and livable cities. Story tips can be sent to