During the period begining in April 2002 through March 2003, a limnological study was carried out in the middle low river basin of the Santa Maria River. Physicochemical determinations and a survey of the communities of the fishes, mollusks and crustacea was performed in five stations in the outlet of the Cañazas River. The physicochemical parameters were performed monthly beginning in August through April. The sampling of biological parameters took place during two consecutive dry seasons, compresing five excursions for each one. Different fishing art and technical were used to collect samples of fauna. Physicochemical variables in general showed small fluctuations along in the river bed; only phosphates exhibited significant changes, while in the outlet of Cañazas River the fluctuations were significant, mainly in the dry stations. Biological communities consisted of the 51 species. Fishes 37 species, including firs report of Arius cookie; crustaceous nine species and mollusks five species. The results indicate that the area studied in the Santa Maria River, presents good water quality which is adecuate for the community of fishes, mollusks an crustaceous.