The River Shannon, Ireland, hydro-electric scheme is described. Catch statistics from smolt index traps, water temperature, and discharge during the smolt migration period are described for the years 1992-1995. No significant differences were found in the performance (measured as recapture rates in the Irish drift-net fishery and return rates to a trap) of coded wire-tagged smolt groups released by helicopter upstream and downstream of the generating station. Over three release years (1991-1993) the overall mortality associated with turbine passage was 8.5%. The significance of night-time generation during the peak period of smolt migration (20 April - 20 May) for the downstream passage of smolt through turbines is discussed.