We develop a model of the travel time of juvenile salmonids migrating through a river r each. The model is derived from an advection–diffusion equation with an absorbing boundary at the downstream collection site. The resulting travel time distribution is determined by two biologically meaningful parameters: migration rate and the rate of population spreading. The model is applied to travel time distributions for 46 cohorts of juvenile spring chinook salmonOncorhynchus tshawytschamigrating through the Lower Granite Pool (52 km in length) in the Snake River. Parameters are estimated using maximum likelihood. A PearsonX2goodness-of-fit test shows that the model is not rejected (∝ = 0.05) for the majority of cohorts.