The objective was to study the effects of increased water temperature characteristic of clearcut watersheds of Pacific coastal streams upon the growth rate of juvenile coho salmon. The natural temperature fluctuations of the stream were used in the study of growth of underyearling fish held in aquariums and fed at various consumption levels. Juvenile coho fed in the control stream grew somewhat faster than did those that experienced the warmer temperatures of the clearcut stream. This was particularly true at low levels of consumption. Growth rates of juvenile coho salmon in the wild state were found to be slightly higher in the clearcut stream as compared to the unlogged stream. This difference from the experimental results may have been due to a change in availability and abundance of food. There was a marked decrease in the cutthroat trout population in the clearcut stream, which may have reduced competition for food. There was no apparent influence of infestation by salmon poisoning fluke on the condition of the juvenile coho in the clearcut stream.