Scales were taken from adult rainbow trout(Oncorhynchus mykiss, previouslySalmo gairdneri)from the Waimarino, Tokaanu, and Hinemaiaia Rivers; these are tributaries of Lake Taupo, New Zealand. The scales showed both widely‐spaced outer, and narrowly‐spaced inner, circulus zones. Although there were no among‐population differences in average circulus spacing in the outer growth zone, there were significant among‐population differences in the inner zone; these two zones are suggested to represent (common) lake and natal‐stream rearing, respectively. The back‐calculated minimum and average lengths at migration of juveniles from stream to lake was similar for all three populations (c. 94 mm and 140 mm, respectively) but there were significant among‐population differences in age at emigration. The scale patterns and stream sampling suggested that most Hinemaiaia River rainbow trout left the river within the first year whereas much higher proportions of juveniles in the other two streams overwintered before emigrating in their second year.