One lone shell of the so-called mystery snail washed ashore last summer at Flathead Lake, the likely source being illegal aquarium dumps into the jewel waterbody.

The first local evidence of the nonnative species, its shell was found on a beach at Finley Point.

Thomas Woolf, Aquatic Invasive Species Bureau chief for Fish Wildlife and Parks, noted the detection during the recent winter meeting of the Upper Columbia Conservation Commission.

“Dumping aquariums is a terrible thing,” Woolf told the Inter Lake after the meeting.

“It’s not just the snails; it’s the plants,” he added. “It’s the fish. It’s all these potentially invasive things — pathogens that could be in that tank.”

Mystery snails remain a popular algae-grazing aquarium species.

Such mollusks thereby are primarily introduced to waterbodies by dumping aquariums into a lake or stream, for example, but could be spread further by boats, according to the U.S. Fish and Wildlife Service.

That is unlike the smaller nonnative faucet snail, which is introduced and spread via boat; the faucet variety has been detected in waters near but not in Flathead Lake, Woolf said.

Other nonnative threats include the highly invasive zebra mussel, which also has not yet been detected in Flathead Lake despite a major uptick in mussel-fouled vessels being intercepted at mandatory boat inspection stations statewide.

Meanwhile, Woolf said the mystery mollusk has a roughly quarter-sized shell that’s easy to spot. It’s known to clog water intakes and screens but hasn’t so far posed a great environmental threat.

Nonetheless, he said, the snails remain unwanted.

“They don’t have major impacts, but they’re definitely not a desirable species,” Woolf said. “A snail shell about the size of a quarter around is something we need to know about.”

“Eradication of a population would be tough,” he added, “but they’re big enough you can actually see them, and grab them, individually.”

Woolf said once the lone shell was found last summer, officials snorkeled along the shoreline and at nearby marinas to see whether more could be found.

None were, but the agency will continue monitoring through ongoing invasive species surveys.

Dillon Tabish, FWP’s regional communication and education program manager, said detection of the snail also serves to highlight the state’s Don’t Let It Loose initiative.

Rather than illegally dump out a tank, residents should contact a pet store or shelter concerning unwanted pets, the initiative advises.

“This is a good opportunity to remind folks not to dump aquariums into bodies of water,” Tabish wrote in an email. “It can cause immense damage.”

Reporter John McLaughlin can be reached at 758-4439 or jmclaughlin@dailyinterlake.com