SUMMARY Lotic species of freshwater algae have a higher respiratory rate in a current as compared with that in still water. Species in 4 classes (Chlorophyceae, Xan‐thophyceae, Bacillariophyceae, Rhodophyceae) were tested. A correspondingly higher uptake of P32 was also noted. The fact that the increase in metabolic rate results from the sweeping effect of a current was indicated by the lower mineral uptake of filaments floating free in a current as compared with that of filaments held still in the current in the same container. The current effect was evident even at current speeds as low as 1‐4 cm jsec.