A paddle wheel rotatable about an axis and exposed to radial inward and crosswise water flow has a hub on the axis and about which the wheel is rotated in a rotation direction about the axis and a plurality of angularly spaced blades spaced radially outward from the hub, forming spaces through which water can flow, and each formed by a plurality of radially spaced arcuate elements each in turn having a radially outer end and a radially inner end. These elements are each concave between the respective ends toward the incoming water flow with the radial outer ends more widely spaced than radial inner ends such that each element forms an acute angle with the adjacent element or elements and the spaces between the blades narrow in a direction of flow of water through them.