Located 16.5 kms. off the western coast of Osa Peninsula in the Pacific Ocean. It can be reached by small boats that are moored along the piers at Bahía, in Ballena National Marine Park or on the banks of the River Sierpe. Bahía is 50 kms. from Caño Island and 189 kms. from San José. Sierpe is 53 kms. from the Island and 291 kms from San José on the Southern Interamerican Highway.
Caño Island Biological Reserve consists of 300 hectares of land and 5,800 hectares of sea. The jagged coastline is 10 kms. long with small beaches of white sand (the largest 400 meters wide), rocky platforms and cliffs up to 60 meters high. In the centre of the island there is a wide plateau, which is divided into two parts by the watershed, no higher than 110 metres, and which is crisscrossed by both year-round and seasonal rivers and streams that plunge down the cliffs to the sea.
The geological history of the island indicates that it is the product of plate tectonic setting, in this case the subduction of the Cocos Plate beneath the Caribbean Plate. The age of this relic mountain is beweetn 40-50 million years.
Despite its proximity to the mainland, Caño island has barely 158 species of superior plants and ferns and provides shelter for just 13 land birds, some species of seabirds, a small number of insects and 7 species of freshwater fish. There are no poisonous land snakes. The coral reefs have been very badly affected by the Niño Phenomenon.
The forests on the island are mainly composed of perennial species of very moist tropical forests. Predominant species in the primary forest are cow tree, believed to have been planted by the native Indians, fig tree, wild cacao, rubber tree and numerous vines and epiphytes.
The birdlife includes the common black-hawk, pale-vented pigeon, Northern phalarope, clay-coloured robin, and several sea birds, such as the magnificent frigatebird, brown pelican, and brown booby which apparently mate and nest on the island.
Although islands tend to have small poulations of amphibians and reptiles due to the fact that these two groups of animals are very susceptible to salinity, Caños Island has a wide variety of snakes: boa constrictors, grass snakes, chunk headed snakes and at least two more species, including the poisonous sea snake. There are also basilisks and green iguanas. Mammals are scarce on the island and are restricted to three species: a marsupial, a bat and the paca, which was introduced.
The water surrounding the island teem with many species of fish similar to those listed at Ballena National Marine Park. Some of the marine mammals are the common dolphin, bottle nosed dolphin, sperm whale, pilot whale and humpback whale, the latter an endangered species with a wide range throughout the world.
The existence of stone spheres, tombs with stone statues, golden votive offerings and plychrome ceramics gave rise to a theory that the island was used as a cementary for important persons during the pre-Columbian period. Remains of domestic pottery and stone farming implements suggest that the island also was inhabited by local indians 500 years ago.
In 1940, the United Fruit Company built a house and a lighthouse on the island that were used until 1961. Today the only residents are officials of the National Parks Service who live at a small base on the coast. The climate is very hot and very humid with average temperatures between 26ºC-28ºC. Rainfall varies between 4,000-5,000 mm with a moderate dry season from January to April.