Reservoirs are a ubiquitous anthropogenic component of river systems and can affect species distributions and river ecosystem functioning. The unique ecotone that is formed at the river to reservoir interface (RRI) is relatively poorly studied. We examined body size distributions of Spotted Gar (Lepisosteus oculatus), a top predator in these food webs, across three RRIs in North Texas. Body sizes were expected to increase across the RRI to reservoirs, except during late Spring and early Summer as fish move into streams to spawn. Trends during Winter support this expectation, but insufficient data inhibit our ability to assess other temporal dynamics.