Waters of the mangrove swamp at Cananeia were analysed bacteriologically aiming the determination of the degree of bacterial contamination. Aerobic counts varied significantly by season, tide and station with the highest of 13,000 and the lowest of 21/ml while coliform counts showed significant variation only by station with the highest of 1,600 and the lowest of 3 per ml. Pseudomonas-Achromobacter group comprised the highest percentage of the total flora at the level of around 60%. The biochemical characteristic of the strains of this group are more saccharolytic than proteolytic, certainly due to the great number of diatoms present.