A great area of wetlands in the Los Guatusos Plain, with a seasonal lake, found just South of Los Chiles, almost on the Nicaraguan border. This area has become marshy due to sedimentation and its lake almost disappears between Febuary and May, the dry period.

This reserve is principally for aquatic bird life, which, of course, abounds there. The nesting colony of olivaceous cormorants (Phalacrocorax brasilianus) in the reserve is the largest in the country. The only permanant population in the country of the Nicaraguan grackle (Quiscatus nicaraguensis), normally considered endemic to the shore areas of Lake Nicaragua, is found here.

 Caño Negro has a rather complete center for wetlands research with complete laboratory, incubators, rescue area and living quarters in the little town of Caño Negro, which has bus connections to San Jose and Los Chiles.