Abstract: A cross-flow water turbine has a casing, a runner, a horizontal inlet and a vertical outlet. The inlet is divided by a pivoted guide vane to form a pair of inlet passages. A horizontally extending admission passage is connected to the casing at the inlet side thereof, and a vertically extending discharge passage is formed as a draft tube and connected to the casing at the outlet thereof. The inlet and the guide vane are arranged such that the inlet flow to the runner is directed downward at an angle of about 40.degree. with respect to the horizontal, and the outlet flow from the runner is directed substantially vertically. At the outlet there are a pair of side spaces on either side of the runner resulting in an increased cross section conforming to the cross section of the draft tube. Both of these side spaces are vented to the atmosphere by a single venting valve so that the suction pressure in the draft tube does not exceed a predetermined value.