The screw turbine – water turbine which uses the principle of the Archimedean screw. The turbine convert the potential energy of water on an upstream level into work. It is compared to the water wheel. The Archimedean screw turbine consists of a rotor in the shape of an Archimedean screw which rotates in a semicircular trough. Water flows into the turbine and its weight presses down onto the blades, and forces the turbine to turn. Water flows freely off the end of the turbine into the river with a relatively low head and on low flows (0.01 m³/s up to around 10 m³/s on one turbine). The turbine is considered to be friendly to aquatic wildlife because of the construction and slow movement of the blades of the turbine.