An arrangement for extracting energy from flowing liquid, such as tidal flows, oceanic currents and water flowing in rivers. The arrangement comprises a support device (12) and a turbine device (1) which is pivotally connected to the support device (12) about a substantially horizontal axis (18). The turbine device includes at least one helical turbine (2; 4), each having an axle connected to an energy converter (22; 24). The turbine device (1) has a proximate end and a distal end, the proximate end being pivotally connected to the support device (12), and the distal end being freely movable in a substantially vertical, circular path in the flowing liquid. This enables the turbine device, in use, to adjust to an operational angle with respect to a horizontal plane. The arrangement is characterized in that the distal end of the turbine device (1) is provided with at least one transverse bar (7), stabilizing the operational angle of the turbine device (1). Various flow guiding devices also contribute to stability and performance of the arrangement.