Carp Cyprinus carpio altered the repertoire of swimming behaviour with increased flume length. While the transition speed from steady to burst–coast swimming was unaffected by flume length, fish reached higher critical swimming speed (Ucrit), consequently swimming for longer periods of time in burst–coast mode and hence performing more work before becoming fatigued. Analysis of swimming behaviour of burst–coast swimming revealed an increase in duration and a decrease in distance of forward burst movements with increasing water speeds. Frequency was unaffected by water speed. Overall, longer flumes increased Ucrit by allowing for less restricted burst–coast swimming behaviour.