The Minnesota Department of Health is threatening to sink an app that calls itself the Airbnb of pools by classifying homeowners' pools rented through Swimply as public. All public pools in the state must have a trained operator, daily inspections and must be built to a specific construction code. The department said it will fine pool owners who don't comply with the statutes.

The Swimply app — which connects wannabe swimmers to a nearby backyard pool — had more than 30 active listings in the Twin Cities on Wednesday.

But at least one longtime listing is no longer active.

Sean Ryan and Ed Piechowski had been renting out the in-ground, 40-foot pool in their St. Paul backyard on Swimply since last summer. They pulled their listing after getting a letter from the state Health Department in July.

The letter, which arrived days after the Star Tribune featured Ryan and Piechowski's "Montrose Moderne" pool in an article about Swimply, said the state no longer considered their backyard amenity "a true private residential pool" since it was being advertised to the public.

The couple faced a penalty of $10,000 and were given 10 days to either comply with public pool statutes or take their listing down. Since then, other Swimply hosts have told Ryan and Piechowski that they received similar letters.

To the state, a backyard pool becomes public once it's been listed on Swimply. Minnesota's administrative rules governing pools say a private pool is one that's "limited to family members or the family's invited guests."

"A homeowner that rents their pool to customers via a sharing economy app or other platform has effectively turned their pool into a public pool," Health Department spokesman Scott Smith said in an e-mail.

"All public pools are inspected regularly by trained environmental health specialists who ensure that the requirements are being met and that the pool is healthy and safe to enjoy," he added. "Potential risks include drowning, illness due to waterborne diseases, or injuries from improper use of pool disinfection chemicals."

Ryan and Piechowski have been talking with state and local politicians, including state Sen. Erin Murphy, and urging Minnesota lawmakers to change existing statutes and create new, sharing economy-specific regulations to make room for Swimply hosts.

"They've been hammering square pegs into round holes, because the statutes identify the difference between a public pool and a private pool, but the statutes don't give any leeway for Swimply," said Piechowski.

"Swimply is good for Minnesota," he added, arguing that the ability to rent out a pool short-term makes it a better investment. "This is good for builders, this is good for pool installers, electricians, concrete workers, the people who dig the holes."

Swimply has faced similar obstacles in other states.

In Wisconsin, where officials have also demanded Swimply pools follow rules for public pools, an organization called Wisconsin Institute for Law and Liberty threatened to sue on behalf of the app this spring, according to an Associated Press article.

Swimply co-founder Asher Weinberger said he doesn't consider backyard pools rented through his app public, "no more than Airbnb homes are hotels or Airbnb pools are public pools."

But currently, Swimply puts the burden of learning about, following or fighting local ordinances onto its users.

"As part of our onboarding process, we advise our hosts to do their due diligence on any local statutes or ordinances," Weinberger said.

Erica Pearson • 612-673-4726