Grassland rivers often flow through intensively managed landscapes, with consequences for ecosystem structure and function, including biotic assemblages and resulting energy flow through their food webs. The Niobrara and Elkhorn Rivers (Nebraska, USA) are similar in watershed size and climate, but differ in their watershed management because the Niobrara is a National Wild and Scenic River. As a result, the Elkhorn is characterized by higher nutrient loads, increased turbidity, and more variable flows compared to the Niobrara. Taking inspiration from Dr. Mažeika Sulliván’s work bridging watershed conservation and food web ecology, we sought to understand how macroinvertebrate food webs differ between these two rivers with contrasting protection status. We sampled eight macroinvertebrate consumer groups common in both rivers (e.g., caddisflies of the family Hydropyschidae, and mayflies of the family Isonychiidae) and estimated their basal resource use via stable isotope analysis. We used a three-end-member Bayesian mixing model to estimate coarse detritus, periphyton, and seston contributions to macroinvertebrate consumer food webs and compared these metrics between the two rivers. Our initial findings suggest that both food webs are primarily supported by coarse detrital resources (81% in Niobrara, 83% in Elkhorn), but likely differed in their diets consisting of periphyton and seston. Specifically, seston was a more important food web resource in the Elkhorn (13% of primary consumer diet), and periphyton was more important in the Niobrara (16% of primary consumer diets), consistent with the relative availability of these resources in each river. Collectively, our food web analysis points to potential switching in basal resource use from periphyton to suspended particles by macroinvertebrate consumers that live in intensively managed grassland rivers, and highlights the utility of food web analysis for detecting nuanced changes to ecosystem structure in response to watershed-scale management approaches.