Aquatic insect assemblages of the Colorado River downstream of Glen Canyon Dam are comprised of generalist taxa, and sensitive EPT taxa have been rare or absent. To mitigate adverse effects of hydropower flows on insect assemblages, experimental Bug Flows were implemented in 2018-2020 and in 2022. The experiment was overall successful in achieving these goals as evidenced by monitoring data showing a more than four-fold increase in caddisfly abundance, a taxon that has occurred in low numbers since the closure of Glen Canyon Dam in 1963. Periods of high abundance for aquatic insects often coincide with improved growing conditions, increased body size, fecundity, and shifts in emergence phenology. In this presentation, we explore these relationships in a Hydropsychid caddisfly (Hydropsyche oslari). We predicted that years of high H. oslari abundance would be associated with earlier emergence, large adult female body size, and greater reliance on high quality (autochthonous) food sources. We measured the length and weight of 241 H. oslari females collected in light traps between 2015 and 2020. We used stable isotope (δ13C, δ15N) analysis to investigate the relative values of autochthonous (terrestrial) and allochthonous (aquatic/algal) carbon and nitrogen in H. oslari diets over time. We found that years of high abundance corresponded with earlier emergence dates and that H. oslari female body size is smaller later in the year, corresponding with diets being more allochthonous later in the year. Length and isotope ratios varied between years, however, both ordinal day and year were significant predictors of length. This analysis of phenological and physiological response of a focal taxa provides insight on the population-level effects of the Bug Flow experiment as a whole.