Costa Rica’s diving is for pelagics. If you’re looking for coral, you’ll be happier in Belize  or the Bay Islands of Honduras . Visibility, unfortunately, ranges only 6–24 meters, but water temperatures are a steady 24–29°C or higher.
Scuba outfitters are located at the principal beaches. In San José , Mundo Aquático (tel. 506/2224-9729, www.mundoacuaticocr.com ), 25 meters north of Mas X Menos, in San Pedro, rents and sells scuba gear. The only hyperbaric chamber is at Cuajiniquil, in Guanacaste.
Most dive-site development has been along the Pacific coast. You’ll see little live coral and few reefs. In their place, divers find an astounding variety and number of fish, soft corals, and invertebrates. Most diving is around rock formations. Visibility can often be obscured (particularly in rainy season, May–Nov.), but on calm days you may be rewarded with densities of marinelife that cannot be found anywhere in the Caribbean.
Favored dive destinations in the Pacific northwest include Islas Murciélagos and the Catalinas. Both locations teem with grouper, snapper, jacks, sharks, and giant mantas, as well as indigenous tropical species. Dozens of morays peer out from beneath rocky ledges. And schools of tang, Cortez angelfish, bright yellow butterflies, hogfish, parrot fish, giant jewfish, turtles, and eagle rays are common. Great bull sharks congregate at a place called “Big Scare.” The two island chains are challenging because of their strong currents and surges.
Punta Gorda dive site, six kilometers west of Playa Ocotal , is known for thousands of eagle rays and whale sharks. Divers also report seeing black marlin cruising gracefully around pinnacle rocks. At Las Corridas, only one kilometer from El Ocotal, you’re sure to come face to face with one of the 180-kilogram jewfish that dwell here. Bahía Herradura has an area known as El Jardín, famed for its formations of soft coral and sea fans.
Uvita , midway down the Pacific coast, has a small coral reef, as does Caño Island , just off the Osa Peninsula. About two kilometers out from Caño is a near-vertical wall and parades of pelagic fish, including manta rays. The island is serviced by dive boats out of Drake Bay  and Golfito . Charters can also be arranged out of Quepos .
Cocos Island  is the Mount Everest of dive experiences in Costa Rica. Its reputation for big-animal encounters—whale sharks, hammerheads (sometimes schooling 500 at a time), and mantas—have made it renowned. Cocos is 550 kilometers southwest of Costa Rica, necessitating a long sea journey on a live-aboard dive vessel.
The Caribbean coast has yet to develop a serious infrastructure catering to sport divers, although dive operators can be found in Cahuita , Puerto Viejo , and Manzanillo . At Isla Uvita, just offshore from Limón , are tropical fish, sea fans, and a coral reef, plus the wreck of the Fenix, a cargo ship that sank within a kilometer of the island years ago.
Farther south, at Cahuita, is Costa Rica’s most beautiful—but much damaged—coral reef, extending 500 meters out from Cahuita Point. The fan-shaped reef covers 593 hectares and has 35 species of coral, including the giant elkhorn. Two old shipwrecks—replete with cannons—lie on the Cahuita reef, seven meters down.
The Gandoca-Manzanillo Wildlife Refuge  protects a southern extension of the Cahuita reef, and one in better condition. If undersea caverns are your thing, check out Puerto Viejo, 20 kilometers south of Cahuita. The best time for diving is during the dry season (Feb.–Apr.), when visibility is at its best. Check with park rangers for conditions, as the area is known for dangerous tides.