The cavitation-erosion (CE) damage features and a microstructural peculiarity of the CoCrFeNi high entropy alloy (HEA) are presented in this paper. While this HEA is theoretically predicted and often experimentally demonstrated to be a single-phase solid solution, noticeable elemental segregation has been observed in both the interdendritic regions and dendrite interiors in this study. This segregation causes a subtle reduction of lattice parameter, and the interdendritic segregated regions are frequently CE damage initiation sites. In the dendrite interiors, oxygen-rich particles with elemental segregation as their wrappings and the small speckles of elemental segregated regions show different CE damage features. In the dendrite interiors, CE-induced martensite formation is negligibly, and slip lines and their intersections are CE damage initiation sites. While a few CoCrFeNi-based HEAs have been shown to be CE-resistant in the literature, the CE resistance of the CoCrFeNi base itself is not high.