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New Zealand Snails Invade Olympia's Capitol Lake

Scientists can get the thrill of a lifetime if they discover a new species.

But after a retired micro-biologist discovered invasive snails near the Washington state capital, biologists are alarmed, not excited.

KUOW's John Ryan reports from the shores of Olympia's Capitol Lake.

 Capitol Lake
Olympia's Capitol Lake.

Allen Pleus didn't discover the tiny species that has invaded Capitol Lake. But he does have to deal with it.

Allen Pleus: "My name's Allen Pleus, I'm the Aquatic Invasive Species Coordinator for the Washington Department of Fish and Wildlife. And I'm standing right now in Capitol Lake.

On the shore behind him, a newly posted sign says the lake is closed to public use. Pleus is in about knee-deep water, in his waterproof hip-boots. He's been splashing around, turning over rocks in the shallows, trying to find Olympia's latest invaders.

Allen Pleus: "There you can see a bunch of them on my hand here, these little ones, these are all New Zealand mud snails. They range in size from about the size of a flake of pepper up to the size of a grain of rice."

Up close, they resemble tiny black screws. They look pretty harmless.

Allen Pleus: "But these things are nasty, and if they take over, your biodiversity is gone."

The snails were discovered just before Thanksgiving. The state quickly closed Capitol Lake to keep the snails from spreading.

The snails apparently arrived in North America with live fish or fish eggs imported for a trout farm in Idaho. They've been found throughout Idaho's Snake River, and in a few spots in Oregon.

In Washington, they've established beachheads in the lower Columbia River and on the Long Beach peninsula.

But until Bert Bartleson discovered the snails, they weren't known to have reached Puget Sound. Bartleson happened to discover the mud snails while he was out birdwatching on Capitol Lake. He collects sea shells for a hobby, but he wasn't happy to add New Zealand mud snails to his collection.

Bert Bartleson: "Aside from the scientific curiosity, it was mostly, 'aw, man, one more invasive species to have to fight.' They can pretty much eat everything, all the little algae get eaten, and everything that eats algae starves to death, and you have nothing but snails."

The snails have probably been in Capitol Lake for a couple years. Their population in the lake could easily number in the millions already.

Wildlife officials' main focus is getting people to avoid spreading the snails to other parts of Puget Sound on their clothing or their gear.

Hundreds of tiny black snails from New Zealand coat a rock from Olympia's Capitol Lake. The few larger snails are the native species.

Pleus starts to tell me how the snails pose a risk to native invertebrates and the salmon and trout that feed on them. But he's interrupted when a small dog trots into the water.

Allen Pleus: "Excuse me, sir?

Man: "Come here, Bacon."

Allen Pleus: "There's these little New Zealand mud snails in the lake that could get, they're invasive, and they can get in the paws of the animals, so we're asking people not to bring them in. But thank you."

Man: "What are they?"

Allen Pleus: "New Zealand mud snails. Thanks."

Capitol Lake makes a scenic backdrop for the Washington State Capitol and downtown Olympia.

But it's hardly a pristine ecosystem. In fact, it's a man-made reservoir infested with noxious weeds. And it's filling up with sediment.

Jeff Dickison is a biologist with the Squaxin Island Tribe.

Jeff Dickison: "This is not the first invasive species there, and I'm sure it won't be the last. Most of them are resulting from the fact that they're trying to maintain an artificial ecosystem there and it just really doesn't work that way when you have a significant river system flowing into Puget Sound."

State, county and tribal officials want to take out the dam beneath Olympia's Fifth Avenue and restore Capitol Lake to what it once was: the tidal estuary of the Deschutes River.

Officials from Tumwater and the Port of Olympia want to dredge the lake and keep managing it as a freshwater reservoir.

The long-term fate of Capitol Lake remains a political football. But in the short-term, the Department of Fish and Wildlife hopes to have Capitol Lake temporarily drained during a cold snap this winter. The mud snails apparently can't handle freezing temperatures.

State biologists did a comprehensive search for the snails upstream on the Deschutes River Dec. 3. They were happy not to find any.

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