An Archimedean screw apparatus for use either in power generation or for the pumping or conveying of fluid material includes a screw body formed by a shaft and at least one helical flight that is located in a close-fitting channel structure. The screw body is rotatably mounted such that the flight is in frictional contact with in inner surface of the channel. The weight of the screw body is borne at least partially by the channel structure and is dissipated fully or partially along the length of channel structure. Hence, preferably the Screw both is either provided with only a single bearing located at one end of the shaft, the other end being left floating within the channel structure, or the screw body is not provided with any bearings and the shaft is connected directly to a drive mechanism or to part of a power generating apparatus.