Caño Island sits roughly 20 kilometres off the Osa Peninsula, and the pre-Columbian people who used it left behind stone spheres on a landmass with almost no permanent fresh water. Those granodiorite spheres, some nearly perfectly round, were carried across open sea by canoe. Archaeologists still argue about why. The island served as a cemetery, not a settlement, and its interior hills were burial ground rather than village. Costa Rica declared the island and its surrounding waters a biological reserve in 1978. The protected zone extends 15 kilometres out from the shoreline, which is why the marine life here differs so sharply from the mainland coast. The reserve is administered by SINAC, the national conservation system, and a conservation fee of 15 USD per person applies to every visitor. Interest in a cano island snorkeling tour from drake bay grew steadily through the 2000s as divers documented what the boundary had preserved. The geology explains the water. Caño Island is the exposed tip of an underwater volcanic ridge, and the basalt and andesite outcrops around it — Bajo del Diablo, Paraíso, Coral Garden — form vertical structure that reef fish colonise in dense schools. Visibility often exceeds 15 metres. White-tip reef sharks rest on sand channels. Green and hawksbill turtles graze the shallows. Humpback whales pass through the corridor twice each year, and dolphins are common on the crossing itself. Coral cover here is Pacific coral, hardier and less colourful than Caribbean reef, dominated by Porites and Pocillopora colonies. Access is deliberately limited. Landing is restricted, the interior trails are largely closed to protect the archaeological sites, and the reserve operates 08:00-16:00 daily. Visitor numbers are capped, which is the central reason the underwater habitat has held its condition while dive sites elsewhere in the eastern Pacific have thinned. Operators running Caño Island snorkeling boat tours depart from Drake Bay on the mainland side, a crossing of roughly 40 to 60 minutes depending on swell. The island now functions as a benchmark. Marine biologists use it as a reference point for what an unfished Pacific reef looks like, and Costa Rica's wider marine-protection policy has repeatedly cited the reserve as evidence. For the visitor, that scientific weight translates into something simpler: a cano island snorkeling tour from drake bay puts you above one of the most intact stretches of nearshore Pacific water in Central America. The address is unglamorous — Caño Island Biological Reserve, Osa Peninsula, Puntarenas — and the reserve's official information line, 2735-5036, is answered by park staff rather than a booking desk.