Exposure to natural ultraviolet radiation has risen in southern Patagonia due to atmospheric ozone depletion. The available literature describes how natural ultraviolet radiation affects the ecosystems, and in aquatic environments ultraviolet radiation can penetrate the water column under conditions of low concentration of substances such as dissolved organic carbon which provide a screen effect by absorbing wavelengths corresponding to natural ultraviolet radiation. The present chapter is a description of literature about the effects of natural ultraviolet radiation in zooplankton populations and communities in the inland water ecosystems of Chilean Patagonia (38-51 degrees S). At the population level, two patterns have been observed: first, the effects in species with a low tolerance to natural ultraviolet radiation exposure, which corresponds with transparent species; and second, the effects in species with photoprotective substances that are tolerant to high levels of natural ultraviolet radiation. On the community scale it has been observed that under high exposure to natural ultraviolet radiation only tolerant species are present, and under oligotrophy it was observed that few species are tolerant, mainly calanoid copepods, which are dominant in zooplankton assemblages.