The Caño Negro National Wildlife Refuge is an area of lowlands that are seasonally flooded forming lakes, lagoons, marshes and holillo groves which supply shelter for 320 species of birds (migratory and non-migratory) depending upon the time of year.

The main lagoon is Caño Negro, which is fed by the Frio River, which flows down to the north of the Arenal Lake Basin.

With the arrival of the dry season, early February through April, it is reduced to small lagoons, channels, streams, ditches and strips of beach inhabited by cattle egrets, wood storks, roseate spoonbills, white ibis, American anhinga, black bellied tree ducks and geotropic cormorants. It is especially important because it provides refuge to the largest colony of neotropic cormorants in the country. It is also the only area where you will find permanent colonies of Nicaraguan Grackle, an endemic bird species from Lake Nicaragua.

The forests, grasslands and marshes provide shelter for cougars, tapirs, jaguars and ocelots which are, unfortunately, endangered species. As well as tayras, 2 and 3 toed sloths, and 4 species of monkeys: howler, white -faced, spider and capuchin.

The rivers abound with tortoises, a large population of Cayman and approximately 30 species of fresh water fish, including the Gar which is considered a living fossil.

Created in 1984, Caño Negro extends over 9,969 Hectares (24,525 acres) of very hot and humid terrain on the Guatusos plain, north of the Alajuela Province, between the counties of Upala (38 Km/23 Miles) and Los Chiles (26 Km/16 Miles).

In 1991, Caño Negro was declared a Wildlife Area of International Importance.

The climate displays the same characteristics of the prevailing conditions of the Pacific and Caribbean, but is more influenced by the conditions of the Caribbean’s pattern of wind and clouds. Heavy rainfall, concentrated between May to January, brings 2,500 mm to 3,000 mm (97.5 to 117 inches) a year.  The average annual temperature is 25 to 27 deg C (77 to 81 deg F).