Boasting over 1,290km (780 miles) of shoreline on both the Pacific and Caribbean coasts, Costa Rica has a rich diversity of underwater flora and fauna.

Whale Shark (Rhincodon typus) -- Although the whale shark grows to lengths of 14m (45 ft.) or more, its gentle nature makes swimming with them a special treat for divers and snorkelers. Prime Viewing: Can occasionally be spotted off Isla del Caño, and more frequently off Isla del Coco.

Green Turtle (Chelonia mydas) -- A large sea turtle, the green turtle has a teardrop-shaped carapace that can range in color from dull green to dark brown. Adults reach some 1.5m (4.9 ft.) and weigh an average of 200kg (440 lb.). Prime viewing: Carribean coast around Tortuguero National Park, from July through mid-October, with August through September their peak period.

Leatherback Sea Turtle (Dermochelys coriacea) -- The world's largest sea turtle (reaching nearly 2.4m/8 ft. in length and weighing more than 544kg/1,200 lb.), the leatherback sea turtle is now an endangered species. Unlike most other turtle species, the leatherback's carapace is not a hard shell, but rather a thick, leathery skin. Prime Viewing: Playa Grande, near Tamarindo, is a prime nesting site from early October through mid-February; also nests off Tortuguero in much lesser numbers from February through June, peaking during the months of March and April.

Olive Ridley Sea Turtle (Lepidochelys olivacea) -- Also known as tortuga lora, the olive ridley sea turtle is the most common of Costa Rica's sea turtles, famous for its massive group nestings, or arribadas. Prime Viewing: Large arribadas occur from July through December, and to a lesser extent from January through June. Playa Nancite in Santa Rosa National Park and Playa Ostional, north of Nosara, are the prime nesting sites.

Moray Eel (Gymnothorax mordax) -- Distinguished by a swaying serpent-head and teeth-filled jaw that continually opens and closes, the moray eel is most commonly seen with only its head appearing from behind rocks. At night, however, it leaves its home along the reef to hunt for small fish, crustaceans, shrimp, and octopus. Prime Viewing: Rocky areas and reefs off both coasts.

Humpbacked Whale (Megaptera novaeangliae) -- The migratory humpbacked whale spends the winters in warm southern waters and has been increasingly spotted close to the shores of Costa Rica's southern Pacific coast. These mammals have black backs and whitish throat and chest areas. Females have been known to calve here. Prime Viewing: Most common in the waters off Drake Bay and Isla del Caño, from December through April.

Bottle-Nosed Dolphin (Tursiops truncates) -- A wide tail fin, dark gray back, and light gray sides identify bottle-nosed dolphins. Dolphins grow to lengths of 3.7m (12 ft.) and weigh up to 635 kilograms (1,400 lb.). Prime Viewing: Along both coasts and inside the Golfo Dulce.

Manta Ray (Manta birostris) -- The manta is the largest species of ray, with a wingspan that can reach 6m (20 ft.) and a body weight known to exceed 1,360kg (3,000 lb.). Despite its daunting appearance, the manta is quite gentle. If you are snorkeling or diving, watch for one of these extraordinary and graceful creatures. Prime Viewing: All along the Pacific coast.

Brain Coral (Diploria strigosa) -- The distinctive brain coral is named for its striking physical similarity to a human brain. Prime Viewing: Reefs off both coasts.

Note: This information was accurate when it was published, but can change without notice. Please be sure to confirm all rates and details directly with the companies in question before planning your trip.