The upstream migration of Atlantic salmon tagged with radio transmitters was analysed on a 6 km long stretch of the River Mandalselva (southern Norway), where the residual flow was 3 m3 s-1. Over a period of 40 days six artificial freshets were released. Two of the freshets lasted continuously for 48 hours and four of the freshets consisted of successive pulses of increased water discharge. There were significant differences in mean migration distance per hour between the freshet period, the 11 hour post-freshet period and the residual flow period for three of the freshets. No clear relationship between increased water flow and salmon migration was found. Mean migration distance per hour during freshets was not different between newly released salmon and salmon that had been in the part of the river with residual flow for some time.