In arid and high-elevation streams of Colorado, dams are necessary for water supply. However, they can alter ecological structure and function with regulated flow regimes and anthropogenic oligotrophy. Didymosphenia geminata (“Didymo”) is a single-cell, stalked diatom species that becomes abundant in phosphorus-limited stream conditions, often below dams. In response to low nutrients, thick extracellular stalks form from Didymo cells and can grow rapidly in attempts to acquire nutrients from the water column. It has been documented that Didymo mats can reduce habitat for macroinvertebrates and disrupt recreation activities. Additionally, through field and laboratory research it has been identified that Didymo is resistant to high-shear environments but grows preferentially in stable flow conditions. However, knowledge gaps exist about long-term food web responses to Didymo-dominated algal communities. The Lower Blue River in Kremmling, CO below the Dillon Dam and Green Mountain Dam is one such example where nuisance Didymo blooms have formed. From 2021 to present, algae, macroinvertebrate, and fish data have been collected every year in May, August, and October. More frequent algae data have been collected since 2023 with paired Benthotorch and velocity measurements. Using this dataset, we evaluated the differences in stable isotopes in macroinvertebrates and fishes across different flow events and seasons and infer the dominance of Didymo associated with other biological data. The study period encompassed drought and wetter-than-average years. We hypothesized that interannual flow variability may predict niche overlap between Brown Trout (Salmo trutta) and Mottled Sculpin (Cottus bairdii) because of significant negative relationships that exist between Didymo and high velocities and discharge which may enhance feeding opportunities for fishes. Preliminary results found that high interannual variability in seasonal patterns, not necessarily predicted by interannual flow patterns, did not inform stable isotope relationships between Brown Trout and Mottled Sculpin. Flow management on regulated rivers may encourage scouring of nuisance Didymo blooms while not affecting higher trophic level patterns, of which knowledge is limited. Yet, future further analysis of fish diets, macroinvertebrate assemblage, and fatty acid content will inform long-term ecological patterns on the regulated Lower Blue River.