The trace element selenium is an essential element with a narrow window between concentrations needed to support life and those that cause toxicity to egg laying organisms. Selenium bioaccumulation in aquatic organisms is primarily the result of trophic transfer through food webs and is poorly predicted by dissolved concentrations in freshwater bodies. To better understand the hydrologic and biological dynamics that control selenium accumulation into fishes of the Lower Gunnison River Basin (Colorado), ecosystem scale selenium accumulation models were developed from data collected between June 2015 and October 2016.