Water and phosphorus (P) exports during the peakflow season increased after a fire in early summer 1998 burned 89% of an upland watershed on the Boreal Plain of western Canada. The change in water export between pre- (1983) and post-fire (1998 to 2000) periods was higher in the burned (4th order) than reference stream (3rd order) (P = 0.01). Burned to reference stream ratios of particulate P (PP) flow-weighted mean concentrations (FWMC) and export were 1.5 and 2.8, respectively, in year 1 and 2.8 and 6.7, respectively, in year 2 post-fire. Particulate P comprised a similar proportion of total P export in the burned stream before fire and in the reference stream (65%), but a higher proportion after fire during the peakflow season only (77%) (P < 0.02). Phosphorus concentration and discharge (Q) were positively related in both streams, across all Q intensities measured in the case of dissolved P, but only at Q > 1.5 m s for PP. Changes in P export after fire were evident during peakflow and were largely restricted to the PP fraction. These changes appear to be driven by higher discharge, which enhanced loading of P-rich particulates from the watershed and (or) from the stream channel.