Yeasts were isolated from 96% of samples taken from five widely separated collection points on the St. Lawrence River during the summer of 1968. Numbers varied from 0 to 9500 per 100 ml but were not correlated with depth (1-ft, 15-ft, and 30-ft depths were sampled) or to salinity. Some influence of time was noted as the numbers were considerably higher in July and somewhat higher in September. The mean numbers of yeasts isolated at Quebec were higher than the means found at the other four stations but the rank varied considerably among the times of sampling. A wide range of species was identified, 39 in 10 genera, and in addition a large number of Candida and Rhodolorula were not classified as to species. Rhodotorula glutinis was the most frequently isolated; the 'pink yeasts' made up 58% of the total isolates.