Streamflow in the River Feshie (106 km2) shows persistent diurnal oscillations from March to June when runoff augmented by snowmelt greatly exceeds precipitation. Diurnal amplitude and maximum daily runoff are comparable to a similar-sized Swiss glacier basin. Daily discharges in the springs of 1979 and 1980 are successfully simulated from daily air temperatures and precipitation using a lumped degree-day model based on Martinec's model but with endogenous snowpack shrinkage at a rate proportional to melting. A best fit of R2= 0.88 was achieved over 53 days in the unusually snowy season of 1979. The biggest errors are in simulating runoff from precipitation for which only lumped data are available. Best-fit parameter values are physically reasonable and only two parameters, describing the initial snowpack, need vary from year to year.