Enhanced loading of nitrogen (N) and phosphorus (P) is pervasive in rivers around the world. As a consequence of nutrient-rich conditions, many well-lit rivers experience severe algal blooms, which pose a threat to water quality and aquatic habitats. Nutrient enrichment in the Upper Clark Fork River, located in western Montana, has increased the productivity of benthic algae, Cladophora glomerata, which routinely forms extensive blooms during summer growing seasons (July – September). We hypothesized that Cladophora influences the character of nutrient limitation by affecting stream structure and surface water chemistry along enrichment gradients. To better understand the impacts of N and P loading on algal proliferation, we deployed nutrient diffusing substrates, collected bi-weekly surface water samples, and conducted algal surveys at four locations. Nutrient diffusing substrates were deployed during the early, mid, and late-growing season (D1, D2, and D3; respectively) to assay potential limitation. After 18 days, chlorophyll-a accumulation was measured as standing crop (mg/m2). Growth responses were assessed using a multilevel Bayesian model to characterize single and co-limitation. Treatment responses 38.5% greater than the control were considered meaningful. During the early, mid-, and late-growing season, all sites were co-limited (D1: 191 – 242%; D2: 237 – 362%; D3: 66 – 254%), with P-limitation decreasing downstream (91% upstream and 47% downstream), concomitant with increased N-availability (N:P = 100 – 30:1). N-limitation was seldom observed but was evident in downstream reaches (D3: 83 – 147%), with greater P-concentration (14 µg/L). Algal cover decreased across Sites 1, 2, 4, except for Site 3 (3 – 30%). Limitation responses followed N:P ratios across all sites throughout the growing season; however, these ratios were poorly predictive of algal cover (R2 = 0.17). These findings suggest that while nutrient availability largely controlled limitation patterns, other factors – such as flow, substrate size, or temperature – may be more influential in determining Cladophora cover.