When is a pool not a pool? When it’s something like the lagoon at Hoakalei, perhaps?

It appears the developer of Hoakalei Resort residences has been snagged again by the nature of the water feature promoted in the sales literature. Haseko Hawaii has had a turbulent history in this regard — the change of plans in what was first planned as Ewa Marina caused a legal battle — when it settled on the current design of the 52-acre lagoon.

And now the state Department of Health is classifying the private community recreational element as a “public swimming pool,” and is holding the management to maintenance requirements it would find impossible to meet.

The solution likely lies in pressing for a reclassification of the lagoon, with its own standards of upkeep — if its private owners want to take up the campaign to get that done.

Health officials had warned Haseko in early May that it would be subject to fines of up to $1,000 a day if it continued to allow residents to swim in the basin. So, at least for the immediate future, “no swimming” signs have gone up at the manmade swimming cove, with water lapping on a sandy beach people find inviting.

The water quality is not the problem, according to Haseko’s own tests. It is the other mandates of Hawaii Administrative Rules governing a swimming pool, which is defined as “any man-made enclosure, structure, basin, chamber, or tank containing an artificial body of water that is used for swimming, diving, or recreational bathing or therapy by humans.”

In such an “open system, the water quality requirements shall be satisfied through pool water circulation,” the regulations state. “The pool water shall be completely exchanged at least once every six hours.” There is also a rule that a high-contrast object be discernable at the deepest point of the pool when looking from the surface.”

These standards seem reasonable for a conventional concrete-and-tile type of pool used at community centers everywhere. This one seems plainly in a different category, possibly a new one.

Haseko contracted with researchers who describe the lagoon as having developed a self-cleaning ecosystem. Unlike a swimming pool filled with water that’s piped in — then emptied and refilled, as required — the lagoon is filled by brackish groundwater that seeps out into the ocean and is replaced by more groundwater, according to a 2014 environmental impact statement. That rate of exchange falls far below the complete water replacement pools require, but the two environments may not be comparable.

As it now stands, the paddleboarding, canoeing and kayaking can continue in Wai Kai Lagoon, an amenity designed to be shared by homeowners and the future guests in the resort accommodations proposed to be developed on the property.

But not swimming. That’s likely a big disappointment to these people, who read the language on the project’s website urging them to “enjoy a day at the beach — at one of the neighboring public beaches or on the sandy shore of Hoakalei’s incredible new Wai Kai Lagoon.”

Haseko executives said they are working to fill the void in the short term by creating a swimming hole adjacent to the lagoon that would meet pool rules and is designing a traditional pool now.

But they also are exploring ways to have some accommodation in state health rules for swimming in a manmade lagoon such as Wai Kai, a pursuit they undoubtedly owe to their homeowners.

Haseko’s public responsibility is to ensure shoreline access, a duty that so far it has fulfilled. But the status of its swimming amenities seems, for now, to be a mainly private matter.

Beneficiaries may want to work to secure that, but it is really up to them to make the case for a refinement to current state regulations. They may decide it’s worth the effort — swimming upstream — to accomplish it.