Many islands, reefs, caves, and rocks lie off the coast of Costa Rica, providing excellent spots for underwater exploration. Visibility varies with season and location. Generally, heavy rainfall tends to swell the rivers and muddy the waters, even well offshore. Banana plantations and their runoff have destroyed most of the Caribbean reefs, although there's still good diving at Isla Uvita, just off the coast of Limón, and in Manzanillo, down near the Panamanian border. Most divers choose Pacific dive spots such as Caño Island, Bat Island, and the Catalina Islands, where you're likely to spot manta rays, moray eels, white-tipped sharks, and plenty of smaller fish and coral species. But the ultimate in Costa Rican dive experiences is a week to 10 days spent on a chartered boat, diving off the coast of Cocos Island .