The influence of agricultural run-off on bacterial populations in a river.

The microbiological quality of the River Riato (Spain) was evaluated. The influence of cattle that roam free in the warm season was marked. The degree of faecal pollution in the river was higher than predicted from the river basin geographical characteristics. The counts of faecal indicators greatly increased when the cattle were allowed to roam free. Counts of enterobacteria and faecal coliforms ranged from 10(3) to 10(6)/100 ml. Faecal streptococci counts were smaller (less than 10/100 ml). Escherichia coli and Pseudomonas aeruginosa were isolated from all samples. Streptococcus bovis was also isolated but not Strep. faecalis.