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Most past studies of river dune dynamics have concentrated on two‐dimensional (2‐D) bed forms, with constant heights and straight crest lines transverse to the flow, and their associated turbulent flow structure. This morphological simplification imposes inherent limitations on the interpretation and understanding of dune form and flow dynamics in natural channels, where dune form is predominantly three‐dimensional. For example, studies over 2‐D forms neglect the significant influence that lateral flows and secondary circulation may have on the flow structure and thus dune morphology. This paper details a field study of a swath of 3‐D dunes in the Rio Paraná, Argentina. A large (0.35 km wide, 1.2 km long) area of dunes was surveyed using a multibeam echo sounder (MBES) that provided high‐resolution 3‐D detail of the river bed. Simultaneous with the MBES survey, 3‐D flow information was obtained with an …