A transporter, provided for two-way transport of water and organisms living in water, such as fish, between an upper volume of water situated at a higher level and a lower volume of water situated at a lower level in relation to the higher level, which transporter comprises: - an upper inlet and an upper outlet adapted to be provided in flow communication with the upper volume of water, as well as a lower outlet and a lower inlet adapted to be provided in flow communication with the lower volume of water, - wherein 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, and wherein the downstream passage comprises a first helical rotor having a thread-direction, which by a flow directed down-streams causes the first rotor to rotate around its axis, and the upstream passage comprises a second helical rotor, which rotors are mutually connected such that the first rotor drives the second rotor in rotation around its axis, and wherein the second rotor has a thread-direction which at said rotation generates a flow directed up-streams, wherein the first and the second rotors are mutually coupled concentrically to each other and the second rotor is driven in the rotation of the first rotor around an axis of rotation common for the rotors, characterised in that the driving first rotor is arranged centrally in a tubular inner housing, and the second driven rotor is arranged peripherally in an annular space between the inner housing and an additional outer housing, concentrically to the inner housing, wherein the rotor being driven forms a helical wall connecting the outer and inner housings of the transporter. - an upper inlet and an upper outlet adapted to be provided in flow communication with the upper volume of water, as well as a lower outlet and a lower inlet adapted to be provided in flow communication with the lower volume of water, - wherein 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, and wherein the downstream passage comprises a first helical rotor having a thread-direction, which by a flow directed down-streams causes the first rotor to rotate around its axis, and the upstream passage comprises a second helical rotor, which rotors are mutually connected such that the first rotor drives the second rotor in rotation around its axis, and wherein the second rotor has a thread-direction which at said rotation generates a flow directed up-streams, wherein the first and the second rotors are mutually coupled concentrically to each other and the second rotor is driven in the rotation of the first rotor around an axis of rotation common for the rotors, characterised in that the driving first rotor is arranged centrally in a tubular inner housing, and the second driven rotor is arranged peripherally in an annular space between the inner housing and an additional outer housing, concentrically to the inner housing, wherein the rotor being driven forms a helical wall connecting the outer and inner housings of the transporter.