Brent McDonald / New York Times News Service

CÔTES DES ARCADINS, Haiti — It was an immaculately clear midsummer morning, a perfect day for diving. No trash had yet washed up on the beach. A dozen volunteers, all excited, some a bit apprehensive, donned flippers and masks and shimmied into the bathtub-warm sea, eager to join a team of eco-divers responsible for surveying, and perhaps one day helping save, Haiti’s endangered coral reefs.

Only one thing stood in their way: For most of them — like Jessika Laloi, 21 — this was their first time swimming in the ocean. Until a few months ago, Laloi had not even known how to dog paddle.

Now she was wading into the ocean in shorts and a tank top, with a life preserver strapped to her torso, a welcome distraction from the tumult of life since her home collapsed in the earthquake a year and a half ago.

“Diving and swimming is a way of showing you that you are in the environment,” Laloi said. “You are part of it. You don’t have to destroy it.”

Environmental degradation is rife in Haiti — deforestation, erosion, pollution — and for the most part it is hard to miss. But for decades the country’s marine environment has suffered unseen. Its extensive coral reef system, an attraction to foreign scuba divers in the 1970s and ’80s, has largely died off — partly from sedimentation and climate change, but mostly from overfishing.

“It’s probably the worst overfishing I’ve seen anywhere in the world,” said Gregor Hodgson, the director of Reef Check, a nonprofit organization in California that monitors reef health around the globe. Hodgson, who has been leading the training of Laloi and her fellow Haitians, said his organization had worked on reefs in 90 countries.

Months after the earthquake that devastated Port-au-Prince, this nation’s capital, Hodgson flew to Haiti to inspect reefs, checking for quake damage. Instead, he found something more alarming: dead coral as far as the eye could see, and almost no fish. He estimates that about 85 percent of the coral reef has died.

In Haiti 54,000 fishermen rely on the ocean for their livelihood, according to the Ministry of Agriculture, which oversees fisheries management. In recent decades, as their usual catches of Nassau groupers and snappers have dwindled and disappeared, many of them have subsisted by netting and spearing small reef fish that keep coral clean of algae. Now those too are almost gone, and the algae have taken over.

On a recent dive near La Gonave Island, Hodgson floated through a wasteland of intact, dead coral, overgrown with algae and sponges and nearly devoid of fish.

Haiti has the second-longest coastline of all the Caribbean countries, yet it is the only one that has not established marine protected areas where fishing is restricted or off-limits, according to the U.N. Environment Program. So Reef Check decided to survey the reefs and propose that the Haitian government create marine parks where fish can feed, grow and reproduce.

“It’s an unusual situation to come into a country where there are no marine ecologists with respect to coral reefs and no marine biology programs in universities,” Hodgson said. “We’re starting from square one.”

Pierre Guy LaFontant, Haiti’s director general of fisheries, acknowledged that overfishing was a problem and said that officials were receptive to the idea of establishing protected waters. But if the government cannot enforce its existing fishing regulations, can fishermen be persuaded to abide by an invisible line in the water?

“That would be my deepest dream,” LaFontant said, “but the reality is totally different. For fishermen, there are no alternatives. Poverty is the law.”

Hodgson argued the fishermen could, in fact, become the project’s strongest supporters. “Once they see the fish coming back, see the fish growing, see a beautiful reef coming back, then they become the ones who protect the reef,” he said.

Under Reef Check’s guidance, once volunteers demonstrate proficiency in swimming and snorkeling, they will eventually be taught to scuba dive, map the reefs foot by foot and count crucial species of fish, urchins and lobsters — basically, anything people like to eat.

The organization began recruiting volunteer divers earlier this year, but the going has been slow. According to Hodgson, only one of 30 applicants selected for a pool test in April could swim half its length. The rest could not swim at all.

But what the volunteers lack in experience, they make up for in passion and curiosity.

“It’s exciting,” Melissa Barbot, 24, an architecture student, said after a snorkel outing. “This is my first time, and naturally, I’m having this ‘wow’ feeling.”

For some students, learning to dive has also proved to be therapeutic.

“When I saw how amazing it is,” Laloi said of her time in the water, “I just forgot that I live in a very ugly zone.”