Underwater, natural illumination typically varies strongly temporally and spatially. The reason is that waves on the water surface refract light into the water in a spatiotemporally varying manner. The resulting underwater illumination field is known as underwater caustics or flicker. In past studies, flicker has often been considered to be an undesired effect, which degrades the quality of images. In contrast, in this work, we show that flicker can actually be useful for vision in the underwater domain. Specifically, it solves very simply, accurately, and densely the stereo correspondence problem, irrespective of the object's texture. The temporal radiance variations due to flicker are unique to each object point, thus disambiguating the correspondence, with very simple calculations. This process is further enhanced by compounding the spatial variability in the flicker field. The method is demonstrated by underwater in-situ experiments.