Locomotor behaviour of particular person rainbow trout (Salmo gairdneri) was observed in a chamber with aspect-by-aspect flows of fresh water and zero, 1, 10, or 30% oil refinery effluent, with a steep gradient between the two flows. Not one of the concentrations brought on statistically important avoidance or choice as measured by modifications in time spent by fish within the four areas of the chamber (upstream or downstream and north or south side). Similarly, the side of entry of the effluent was not associated to any differences in relative exercise in the 4 areas, as measured by the numbers of movements fish made inside the areas. When 30% effluent was current, the general level of activity in all components of the chamber appeared to be decrease than activities for the opposite concentrations, however the difference was at the borderline of statistical significance (P=0.06). Behavioural response to the effluent was less necessary than direct physiological effects on trout, beforehand documented with the identical effluent. The examined batches of effluent had an total three-day LC50 of about a hundred% effluent. The effluent exceeded Canadian laws in average degree of ammonia, was somewhat elevated in oil-plus-grease and residue, but was well under regulatory limits for phenols and sulphides.