The morphology, flow and process mechanics of river dunes has attracted much interest over many years. However, many of these studies have concentrated on investigating two-dimensional (2D) bed features and their associated flow structures and bed stress distributions. This morphological simplification imposes inherent limitations on our interpretation and understanding of dune form and flow dynamics, as natural dunes are invariably three-dimensional (3D) with an associated fully 3D flow structure. For example, studies over 2D forms neglect the significant effect that lateral flow and secondary circulation may have on the flow structure and thus dune morphology. This paper details a field investigation of the interactions between the 3D morphology, 3D turbulent flow structure and suspended sediment movement over large alluvial sand dunes in the Rio Paraná, NE Argentina. Fixed point and moving vessel surveys enabled the links between three-dimensionality, large-scale turbulence and sediment suspension over the dunes to be investigated.