WHITE CITY — Non-native Chinese mystery snails once again have raised their mollusky little heads in two isolated White City ponds that were poisoned at low levels last year in Oregon's first attempt to eradicate the invasive pest.

WHITE CITY — Non-native Chinese mystery snails once again have raised their mollusky little heads in two isolated White City ponds that were poisoned at low levels last year in Oregon's first attempt to eradicate the invasive pest.

Thursday's discovery sets up a new plan that calls for a heavier dose of poison and plenty of hungry crustaceans to wipe these wayward snails out of the Jackson County Sports Park ponds, which some nitwit likely infested by dumping the contents of a snail-laden aquarium.

A second and heavier dose of copper sulphate likely will come this summer, followed by the planting of native signal crayfish known to treat these snails as Chinese dinner — even if they're hungry an hour later.

"That's one of the options we'll probably be looking at," says Rick Boatner, who heads the aquatic invasive species program for the Oregon Department of Fish and Wildlife.

"We'll give it a try and see if we can knock them back enough to let those crayfish do their thing."

Cipangopaludina chinensis, as they are known by scientists, are somewhat commonly found in aquariums or outdoor water features because they eat algae.

Yet they are banned in Oregon as one of hundreds of exotics that are illegal to possess or sell here.

Though prohibited, they occasionally are found for sale in pet stores.

Mystery snails are large, with adult shells measuring 21/2; inches tall, and they contain a trapdoor-like feature that allows them to effectively seal themselves off against predators and last a long time out of water.

A local angler found the snails in 2009 at the ponds off Kershaw Road, but they are rare in Oregon and they were not positively identified until last summer.

Boatner's invasive species team last year surveyed neighboring ponds and other waterways within the Whetstone Creek drainage — including the Denman Wildlife Area — but found no other snails.

Crews then sprayed the ponds with copper sulphate at about 10 percent of the concentration allowed by federal application standards, Boatner says.

Dead snails were carted off and destroyed.

But that initial lower-the-dose-the-better didn't work.

Recently, an angler again reported seeing the snails, so Dirk Patterson and Sam Dodenhoff of the ODFW invasive species team based in Central Point inspected the ponds Thursday.

Though the water was high and murky, "there were quite a few along the shoreline," Patterson says.

Later this summer, Boatner expects to have ODFW crews again use the copper sulphate, but likely at a dose that's about 50 percent of the maximum dose, he says.

Then non-native ringed crayfish now present in the pond will be trapped out and replaced with the native crayfish that a University of Washington study shows will actively feed on the Chinese mystery snails as a possible long-term control strategy, Boatner says.

"We'll have to just see what happens," Boatner says.

Reach reporter Mark Freeman at 541-776-4470, or email at mfreeman@mailtribune.com.