The vertical distribution and swimming direction of 2-year-old smolted Baltic salmon Salmo salar, kept in circular tanks containing either fresh or brackish water, was monitored for a year. Fish in both groups were distributed in the upper part of a water column and moved with the current during the first part of the experiment, May to August. Salmon kept in brackish water continued this behaviour throughout the year whereas fish maintained in fresh water changed their behaviour drastically. From September, freshwater fish were distributed close to the bottom and tended to swim against the current. The following spring (April-May), fresh water kept fish again started to swim high in the water column, indicating a repetition of smolt behaviour. The results correspond well to the known behaviour of salmon in nature. Apparently, there is an interaction between alternative circannual programs in Baltic salmon; the selection of a specific program is suggested to be based in part on the environmental information the fish perceive.