Since the early 1990’s, water releases from Glen Canyon Dam (GCD) in the Colorado River have been stabilized. These reduced daily flow fluctuations have coincided with a marked decrease in the historically dominant macrophyte, Cladophora glomerata, which has acted as a host for the epiphytic algae that comprises the base of the riverine food web. Twenty years of megadrought in the region have further threatened individual species and the stability of the river food web. In spring 2021, we documented capture the impact of an early spring flow release on the diatom assemblage below GCD. We deployed experimental surfaces to capture diatom colonization patterns prior to increased flows in March. Following the high flow event, we resampled the surfaces to determine the impact of the high flow event on early spring diatom assemblage structure. During the flow experiment, water depth and orientation of the banks but not distance from the dam, influenced biomass recolonization after the high flow rate event. Biomass following the high flow release was strongly related to depth, and secondly to position on the north vs. south facing banks of the river. Diatom valve abundance displayed the same patterns, and mean abundances of the 10 most abundant species was altered by depth. Alpha (Shannon) diversity was also significantly different pre- and post-experimental flow release in relation to depth, but not distance from GCD. The depth at which experimental surfaces were deployed altered duration of exposure to atmospheric conditions. Only the surfaces deployed at the deepest sites were submerged for the full duration of the pre- and post-experimental release periods, therefore decreases in biomass and diatom valve abundance may be related to degree of atmospheric exposure.