ASIDE FROM BEING the worst divemaster I've ever encountered, the guide who led us into the deep waters off Cuba's western tip was also a bobo. A bobo is a cherished Cuban type, someone who is deliberately, defiantly, entertainingly full of it. In this case the divemaster was a laughing complainer who evaded all our questions, skipped the safety briefing entirely so he could smoke a cigarette, didn't bother telling us where we were going, and said of the marine life we might encounter under the surface, "Fishes we will discuss later." He also looked ridiculous in his pseudo-Speedo.

But the water … ah, the water. River sediments make diving off the beaches of eastern Cuba unimpressive, but here in the arid west, facing straight toward Cozumel at a small resort called María la Gorda, upwellings of clean water and marine life from the Cayman Trench create some of the best diving in the Caribbean. Every ripple of sand seemed just beyond reach, even though it was 30 feet away.

I quickly found myself in a bubble bath. My vest, regulator, and backup regulator were all streaming air. "All equipment leaks in Cuba, always," the diver next to me said. He was a blond New Zealander in his twenties, named Ryan. He suggested we team up—something the divemaster hadn't bothered with—and we plunged downward, following the other divers as the shelf fell away into one of Cuba's steep walls, or veriles, an express ride to the bottom of the Caribbean.

The divemaster led us to a narrow crack in the sand, a kind of crevasse in the sea floor, and without looking back he and the others plunged in, with Ryan and me a distant last. The descent was almost vertical, the canyon walls tight and lined with long trees of black coral, one of the slowest-growing, most endangered of all corals. He hadn't mentioned that we were heading right into one of Cuba's most famous black coral formations, thousands of years of creeping progress now vulnerable to any flailing goofball in a wetsuit.

This old-growth forest seemed like an argument for Cuba's conservation policies—the global trade in black coral is restricted under Schedule II of the CITES treaty, precisely because it's been stripped from places like the Cayman Islands and the Yucatán. But back in Havana, I found pearls of the coral selling in the gift shop of the Havana Libre hotel for a dollar apiece. Cuba's government has allowed itself to do many things—like netting dolphins and selling them to global water parks, as it did in the 1990s—that would be condemned if done by private interests.

I managed to slide out of the canyon without crushing anything, but just as I came into open water, my left ear blew. I twisted, gasped, and forgot my buoyancy. I drifted down to 100 feet, alone but for Ryan, watching from afar. The pain was taking me away from things—too deep, too unsafe, breathing too fast (oh, panic!)—but I closed my eyes and managed to correct my depth, following Ryan slowly along the wall, past ten-foot-long pencils of coral, raging purple wrasses, and queen angelfish. An octopus peeked out from below a rock; huge coral jugs littered the wall, a healthy reef buzzing in an emerald-and-blue kingdom.

By the time we made it to the boat, the divemaster was already on the bridge, smoking. We never got a discussion of "the fishes," and back on land, when I asked his name, he stalked off without comment. Accountability is not the Cuban way. As if to emphasize the point, a careless crewman slammed an oxygen tank onto my foot and grinned helplessly under my barrage of curses.

There is a lot of talk about what will happen when American tourists can visit Cuba, but the Europeans and Canadians are already here, 2.3 million of them a year, pouring roughly $2 billion into the island, according to The Economist. Over the past ten years, Cuba has doubled the number of hotel rooms to 50,000, often bypassing environmental concerns in the process. On the hotel-strewn Varadero peninsula, two hours east of Havana, reserves of coconut palms have been bulldozed to accommodate hotels. On the north coast, in 1988, the government rammed a 17-mile causeway through shallow bays to the pristine barrier island of Cayo Coco and then built a string of resorts with 3,000 hotel rooms. Dozens of species of birds and fish were damaged severely; across Cuba, biologists, archaeologists, fishermen, and dissidents told me that Cayo Coco was the spark for their green activism, the first time they saw the environment as a political problem. Today the causeway is dotted with police posts that turn away ordinary Cubans, the ultimate example of what Frommer's calls the "apartheid-like tourist sites" where foreigners languish at a remove from the island's reality.

María la Gorda—Fat Maria—was isolated by geography, price, policy. There were no Cuban guests at the little resort, which had a decent beach, nice cabins, and great sunsets. But the food was pathetic, a steam-table array of hot-dog salads, chicken à la defector, and oily fish, much of it recycled at breakfast. This is typical of Cuban resorts, in my experience at least, and explains why Cuba enjoys one of the lowest return rates in international tourism. Everything from aircraft landing fees, among the highest in the world, to a special tourist peso (expensive on the island, and worthless off it) makes travel outside the resorts difficult and slow.

Ryan sounded disillusioned. "We spent four days in Havana," he told me as we washed our equipment, "and we reckon that was four days too many." He imitated the cigar vendors and would-be pimps: "He-joe my fren' my fren' you wanna Habana cigar girlfren' mulatta negra rubia." He and his friends had liked Viñales, the tranquil tobacco country of the west, but this was the only spot they could love. The water was warmer than in New Zealand, and there were no hustlers, bureaucrats, or even Cubans under the waves.