The erosion of weak, cohesive rocks by the force of water in a river. The effect of this force depends, among other factors, on the strength of the bed, the percentage of clay in the bed, and the velocity and turbulence of the water. Fluid-stressing is effective for weakly cohesive muds, ‘where the current may initiate its own defects’ (Gibling and Tandon (1997) Sedimentol. 44). Evorsion is an alternative term.