Characterizing the habitat of large, navigable rivers is difficult, yet this information is critically important to the conservation of a variety of resident aquatic species. We used low-cost sonar habitat mapping to map benthic substrates throughout nearly 1000 km of four Coastal Plain rivers in Georgia and to quantify the distribution of rocky substrates that may serve as potential spawning habitat for two imperiled sturgeon species, the shortnose sturgeon (Acipenser brevirostrum) and the Atlantic sturgeon (Acipenser oxyrinchus). Although we identified hard, rocky substrates in roughly half of the river km suggested by previous researchers as potential spawning zones, mapping revealed hard substrates in many other locations as well. Our approach provided a detailed view of the distribution, configuration, and extent of these habitats across the riverscape; these results can be used to support future research to gain a better understanding of other key factors associated with spawning habitat selection and habitat change over time. The ability to train novice technicians to execute all phases of the mapping process, and the overall classification accuracy achieved (82%) in this study demonstrated the practicality of this methodology for providing the spatially explicit, and continuous perspective of habitat required for effective conservation across the freshwater range of migratory species like sturgeon.