Ecological studies of big rivers are often confined to small, potentially inadequate spatial scales due to the logistical challenges of sampling these large and often remote environments. To overcome these challenges, we collaborated with hundreds of river based recreationists to sample the abundance and diversity of adult aquatic insects throughout the Colorado River basin. These citizen scientists deployed light traps each night in camp along more than 2,500 river kilometers on the Green, Colorado, Yampa, Gunnison, Dolores, and San Juan Rivers. This collaboration yielded 3,401 light trap samples from 1,667 unique sites from 2015--2016. In this thesis, we hone in on the species and genetic-level diversity of the net-spinning caddisflies (Trichoptera: Hydropsychidae: Hydropsyche spp). In chapter 1, we investigate and model the basin-wide distribution of Hydropsyche and model their occupancy, abundance, and morphology relative to river network structure, flows, water temperatures, dams, and dam management practices. We found that distributions were best predicted by an interaction of mean daily stage change fluctuations, water temperature, and latitude. In chapter 2, we examine the role of river network connectivity on mtDNA CO1 genetic diversity of H. oslari, the most widespread species of Hydropsyche in our study area. We found that populations nested in a dense network of perennial tributaries had more shared haplotypes and less nucleotide diversity (pi = 0.001 -- 0.008) than populations in an arid and less hydrologically connected region (pi = 0.014 -- 0.028). By combining species level ecological modeling and molecular techniques, our results provide insight into the diversity, distribution, and dispersal of aquatic insects in a fragmented riverscape and demonstrate the power of citizen science as a tool for ecological investigations in big rivers.