While the Río Paraguay Basin is sparsely populated, poorly surveyed, and has experienced relatively little human disturbance, it currently faces one large development project: the Hidrovia Paragua-Parana, which proposes to dredge and channel extensive portions of the Río Paraguay watershed, altering water flow and seasonal flooding cycles. Conservation International’s rapid assessment team aimed to document aquatic diversity and the state of the aquatic ecosystem in order to determine sustainable conservation and development strategies for the region—resulting in critical new knowledge of the area’s ecosystem.