Is a Wildlife refuge, part of the Arenal Huetar Norte Conservation Area, in the northern part of Costa Rica twenty kilometers south of Los Chiles near the border with Nicaragua in the Alajuela province. The refuge is a wetlands site that is home to many migratory waterfowl during part of the year, centered on Lake Caño Negro which is fed by the Frío River during the rainy season.
There are no public facilities at the refuge, and the area can be explored only by boat.
The forests, grasslands and marshes of the area provide shelter for various endangered species such as cougars, jaguars, tapirs, ocelots, peccary and several species of monkey (Panamanian white-faced capuchin, mantled howler and Geoffroy's spider monkey), as well as many others. In the dry season the river is reduced to little lagoons, channels and beaches which gives home to thousands of migratory birds of many species such as storks, spoonbills, ibis, anhingas, ducks and cormorants.