A water turbine used in river water which is comparatively rich in soil and sand particles. In order to improve the resistance to erosion due to cavitation, as well as erosion caused by mechanical action of the soil and sand particles, a water contactable portion of the water turbine, in particular a portion of each moving blade which tends to be eroded is formed of a stainless steel containing 0.07 to 0.2 wt % of C, not more than 2 wt % of Si, 7 to 15 wt % of Mn, 1 to 7 wt % of Ni, 10 to 25 wt % of Cr, 0.1 to 3 wt % of W, and the balance substantially Fe and inevitably accompanying impurities.