The Caño Negro Wildlife Refuge occupies an area of 9,969 hectares with characteristics typical of wetlands, and is located in the Río Frío Basin. This is an area of great ecological, economic and social importance for Costa Rica, so much so that in 1984 it was declared to be a wildlife refuge and in 1991 it was included in the RAMSAR list, an organization that protects wetlands of international interest.

There is a system of lagoons, rivers, flood forests, yolilo palms, Santa María plants, marshes and seasonal flooding areas in the refuge. It’s environment is characteristic of the northern zone that borders Nicaragua. But the main characteristic of Caño Negro is that it has the largest natural lagoon system in the northern zone, which covers 900 hectares.

As far as the richness of the biological diversity, there have been 307 species of birds, 78 of mammals and 96 of reptiles have been reported in the refuge, in addition to more than 300 plant species grouped in 73 families of shrubs and trees. However, according to a 1988 study by the Organization of Tropical Studies (OTS), there are 1,016 plant species and 5,000 animal species in the refuge.

The OTS claims that the wildlife is represented by 405 bird species, of which 50 are aquatic birds that are peculiar to wetland habitats. Among these are the: osprey (Pandion haliaetus), woodpeckers (Picumnus olivaceus, Dryocopus lineatus, Malanerpes rubricapillus), hummingbirds (Amazilia tzacalt,Hheliothyx barroti), comorants (Phalachrocorax olivaceus) roseate spoonbill (Platalea ajaja), storks (Jabiru mycteria), green egrets (Butorides virescens), herons (ardea herodias, casmerodius albus, egretta thula), wood stork (Mycteria americana), broad-winged hawk, roadside hawk, common black hawk (Buteo platipterus, Buteo magnirostria, Buteogallus anthracinus), white ibis (eudocimus albus) green kingfisher (Chloroceryle americana), sungrebe (Heliornis fulica) and the black-bellied whistling duck (Dendrocygna autumnalis).

Insofar as mammals are concerned, 160 species have been reported, of which 60 are land animals and 90 are bats. The most important land animals are: peccary (Tayassu pecari), jaguar (Phantera onca), raccoon (Procyn lotor), coati (Nasua narica), puma (Felis concolor), porcupine (Coendon mexicanus), collared peccary (Tayassu tajacu), guanta (Agouti paca), white-tailed dear (Odocoileus virginienus), opossums (Didelphis marsupilis, Chironectes panamensis, Philander opossum), which are species that depend greatly on corridors of vegetation to be able travel through the area.

There are also 60 species of reptiles, including the caiman (Caiman crocodiles chiapasius), turtles, iguanas, lizards and snakes. In addition there are 40 species of amphibians and 4,731 species of insects.

The ichthyic fauna includes 25 fish species, of which four are outstanding for their commercial value, all belonging to the Cichlidae and Lepisosteidae family: tarpon (Megalops atlanticus), snook (Centropomus pectinatus), bass (Micropogonias furnieri) and alligator gar (Xenentodon canaila).