Transporter and fish lock including an upper inlet and an upper outlet adapted to be in flow communication with an upper volume of water, and a lower outlet and a lower inlet adapted to be in flow communication with a lower volume of water. The upper inlet and the lower outlet communicate via a downstream passage having a first effective through-flow area, and the lower inlet and the upper outlet communicate via an upstream passage having a second effective through-flow area. The downstream passage includes a first helical rotor having a thread-direction that by a flow directed downstream causes the first rotor to rotate around its axis. The upstream passage includes a second helical rotor, wherein the rotors are mutually connected such that the first rotor drives the second rotor in rotation around its axis, and the second rotor has a thread-direction that upon rotation generates a flow directed upstream.