The River Fortun is situated in south-western Norway and is typical of the ®ord landscape catchments with large areas above 1000 m a.s.l, steep valley walls and an alluvial river plain at the valley ¯oor. It was regulated for hydropower in 1963 and is Norway's 10th largest regulation scheme. The hydropower scheme has resulted in a large reduction of the frequency of large magnitude ¯ood events. This paper describes the long-term geomorphological response of a gravel-bed river channel to this regulation. The study was initiated after complaints from local farmers of an increase in ¯ooding of farmland after regulation. Forty-seven cross-pro®les of the river repeatedly measured in 1973, 1989 and 1995 along a 1600 m reach have been used to quantify aggradation and degradation in the reach. The pro®les show a reduction in channel size and capacity since 1973, with a net aggradation of 12000 m 3 . The upper part of the reach has been subject to the greatest amount of aggradation, with the river bed being raised by up to 1.5 m, while the lower part has degraded, with lateral erosion cutting banks back by up to 30 m. Aerial photographs from 1964 and 1984 show that former gravel-bars and ¯ood channels have been subject to vegetation encroachment. The hydraulic model HEC-2 was used to compute the water level in 1973 and 1989. The water level has been raised by 0.6 m at low ¯ows in the upper parts of the studied reach. This corresponds to an increase in discharge of between 20±30 3 / s. Overbank ¯ow therefore occurs at lower discharges today than prior to regulation.