This dataset provides sediment concentration and grain size distribution measurements from suspended and bed sediment samples collected in the Atchafalaya River Basin as part of the Delta-X Spring campaign between March 24 to April 2, 2021. During the field campaign, samples were collected in the main distributary channels and the interior of Mike Island in the Wax Lake Delta, Louisiana. Sediment samples were collected from a boat using a Van Dorn sampler (for suspended sediment samples) or a Ponar bed sampler (for bed samples) in the Wax Lake Delta. Suspended sediment samples were collected from a boat drifting at approximately the same velocity as the water flow. One sample was collected per drift. Bed samples were collected in a similar fashion. Data includes measurements of sediment grain size, total sediment concentration, as well as water temperature, velocity, salinity, and depth. The data are provided in comma-separated values (CSV) format.