Fish tracking and anecdotal observations of fish abundance led Nez Perce Tribe Fisheries to infer the presence of a fish passage barrier for upstream migrating steelhead at a particularly steep and confined reach of the South Fork Clearwater River. NHC was subcontracted to develop a detailed 2D hydraulic model showing velocity distributions across a wide range of flows to evaluate the timing and persistence of barrier formation. We surveyed the reach using a combination of UAV (drone) photographs and traditional total station methods. Using Structure from Motion (SfM), a photogrammetric technique used to create 3D models and ortho-imagery from overlapping photographs, more than 2,000 UAV photographs were processed to develop an extremely detailed (two-inch grid size) terrain of the exposed riverbed. Combined with underwater bathymetry, the terrain model was the basis for a 2D hydraulic model that provided a robust foundation for biological fish passage evaluation revealing barriers at certain flows. SfM-derived terrain and ortho-imagery allows the client to visualize the modelled river conditions.