When traversed by a flow of water, a hydraulic machine rotating part rotates around an axis of rotation. It includes runners which are distributed around the axis of rotation and each extend between a leading edge and a trailing edge. Each runner can include a first part which defines its leading edge and a second part which is attached to the first part and defines the trailing edge at least in part. The second part can be elastically deformable or displaceable in a reversible manner with respect to the first part, under the action of the flow of water, the second part defining, when the machine operates, the direction of the flow of water downstream of the runner.