Caño Island was a burial ground long before it became a biological reserve. Pre-Columbian peoples of the Diquís region ferried their dead across roughly twenty kilometres of open Pacific to inter them on this forested plateau, leaving behind granodiorite spheres whose purpose archaeologists still debate. The mainland they launched from is the same coast that Cano Island Snorkeling Tour From Manuel Antonio tours depart from today. Little else about the crossing has changed: the same swell, the same volcanic rock rising abruptly from deep water, the same silence once the engines cut. Costa Rica declared the island and its surrounding waters protected in 1978. The land portion covers roughly three hundred hectares; the marine zone around it is many times larger, and it is the water, not the shore, that draws visitors. SINAC, the national conservation service, has since closed the interior trails to general visitors, largely to shield the archaeological sites from looting. What remains open is the reserve's marine perimeter and a single landing beach, accessible daily from 08:00 to 16:00 under a 15 USD conservation fee per person. Geology explains the clarity. The Sierpe and Térraba rivers push silt along the Osa Peninsula's mainland shore, clouding the shallows near Drake Bay; Caño Island sits far enough offshore to escape most of that runoff. Five coral platforms fringe its eastern and southern shelf, built by hardy Porites and Pocillopora colonies that tolerate warm, shifting Pacific conditions. Around sixty reef fish species patrol them. White-tip reef sharks rest in sand channels between coral heads, spotted eagle rays cross in loose formation, and hawksbill and green turtles surface for air before dropping back toward the gorgonians. Isla del Caño snorkeling trips exist because of this shelf, not because of the island itself. Its position matters as much as its reef. The reserve has drawn marine researchers monitoring coral recovery across the eastern Pacific, and the ranger station logs species that rarely appear along the mainland coast. Travellers weighing Osa Peninsula reef excursions against Corcovado's forest circuits are, in practice, choosing between two halves of one protected system: canopy on the peninsula, coral offshore. Cano Island Snorkeling Tour From Manuel Antonio tickets buy passage to the marine half — a plateau of about 110 metres, a rock standing alone in open water, and a reef that survives in large part because so few people are permitted to stand on it.