It was planned as a boat marina. Then it became a recreational lagoon with no swimming allowed. But many people want a 52-acre body of water in Leeward Oahu to become something else.

A Change.org petition advocates that the predominantly freshwater lagoon dug into coastal Ewa Beach land at Hoakalei Resort be modified so that it’s more like the Ko Olina Resort & Marina lagoons with a big opening to the ocean.

Proponents of the idea claim such a change would resolve a problem that arose in May when the state Department of Health told the developer of the largely residential Hoakalei Resort, Haseko Hawaii Inc., that it faced fines up to $1,000 a day if people were allowed to continue swimming in the lagoon.

The Health Department, after looking into unfounded complaints about toxic algae and possible mosquito breeding in the water, decided that the lagoon met the legal definition of a public swimming pool but didn’t meet pool water circulation standards.

Originally, Haseko excavated the site for a boat marina but stopped short of creating an entrance channel and announced in 2011 that a lagoon was a better idea that would appeal to more residents and visitors, including the general public.

The developer said it intended for its 20-foot-deep Wai Kai Lagoon to be used for stand-up paddleboarding, windsurfing, sailing and canoe paddling, while swimming would be designated for a shallower 1-acre hole still planned next to the lagoon. Yet people took to swimming in the lagoon, and Haseko put out floating play equipment, including a slide not far from one sandy bank that encouraged swimmers.

Hasheme Trevino, one of about 1,500 Hoakalei homeowners, wrote in a supportive petition comment that she was promised the lagoon as an amenity when she bought a home in 2015 but now considers the situation a mess.

“Help make it safe by forcing Haseko to do the right thing to open it up to the ocean,” she wrote.

About 480 people have backed the petition.

Erik Pegg, who bought a Hoakalei home last year, created the petition, in which he claims that nutrient-rich fresh water feeding the brackish lagoon could produce a toxic algae bloom and that the lagoon could become a breeding ground for mosquitoes that spread diseases such as dengue fever.

These issues, some Hoakalei residents believe, could become a liability when Haseko finishes developing the community and turns over ownership of and responsibility for the lagoon to the community association.

Sharene Saito Tam, a Haseko vice president, said the company diligently researched options for the lagoon and found the best scenario for everyone is to keep it the way it is.

The lagoon contains 300 million gallons of water naturally fed by fresh groundwater that mixes with 25 percent seawater seeping through rock under the coast.

DIGGING IT

The developer began digging the basin in 2003 and finished in 2008. Haseko’s plan since the early 1990s was to create a marina as the community’s defining centerpiece, but the company changed course in 2011 partly based on what it said was reduced interest from boaters and prospective hotel operators. Haseko also said legal challenges to creating the harbor channel were factors.

In 2012 marine scientists Marlin Atkinson of the University of Hawaii and Steven Dollar of Marine Research Consultants Inc. produced a report to address how lagoon water quality could best be maintained.

The report focused on what is typically a freshwater stream plant in Hawaii, Chara zeylanica, that somehow had gotten into the lagoon and covered almost the entire floor. Chara has a beneficial presence by consuming nutrients and preventing unwelcome algae blooms. However, the report said if the Chara grew too tall, it could decay, and that might produce noxious odors “making the lagoon increasingly unpleasant, and potentially unusable for human activities.”

Decaying Chara also would release nutrients and potentially feed an algae bloom that could turn the lagoon green, the report said.

The report recommended removing 1 million pounds of Chara, about a quarter of what was present, followed by annual removal of half that amount to keep Chara growth at a beneficial level.

Atkinson and Dollar estimated a $254,000 one-time removal cost and $104,000 for annual maintenance.

Haseko removed the million pounds of Chara in 2012 and said it hurt water quality. Since then no Chara has been removed, and Haseko said water quality has been nice — even better than Ko Olina.

‘REAL SWEET SPOT’

Heather Spalding, a University of Hawaii phycologist, or algae expert, who was retained to monitor Chara and lagoon conditions for the past four years, said the plant has maintained a natural equilibrium where it is beneficial and not detrimental.

“It’s in a really sweet spot,” she said at a community meeting in May at the lagoon. “It’s very stable.”

Dollar, an oceanographer, agrees. In an interview he said, “What’s happening right now looks like the opposite of a perfect storm — it’s a perfect situation.”

At the community meeting, Deanna Pegg, whose husband started the petition, said lagoon conditions in her view resemble an ongoing experiment that gives her long-term concerns.

The Peggs and some other homeowners fear that after Haseko develops hotel buildings and a retail complex with landscaping next to the lagoon, fertilizer-rich runoff could fuel harmful algae blooms.

Making the lagoon a marine environment, they argue, would address that issue.

“We really don’t know until all the landscaping is in place how this ecosystem is really going to work long term,” Pegg said at the meeting.

Saito Tam said Haseko has strict rules and development plans to avoid rainwater and irrigation runoff entering the lagoon. She also said creating an ocean connection would kill the Chara and ruin what is a perfectly good lagoon environment.