For migratory species, successful navigation is critical to fitness. In Atlantic salmon, for example, there is evidence that during migration from natal streams to the sea, passage through waters with poorly defined or mixed water velocity patterns may constrain directional navigation, causing individuals to become trapped or delayed in lakes or other bodies with slowly flowing water. In this study, we determined the minimum water velocities needed to elicit a behavioural response, in this case a change in the direction of holding position, in both wild origin and domesticated salmon smolts. Smolts required a directional flow in excess of 8.9 cm s