This dataset contains water surface elevations collected from boat surveys performed on August 24 and September 22-25, 2021, across the Atchafalaya and Terrebonne basins in the Mississippi River Delta (MRD) floodplain, during the Delta-X Fall 2021 deployment. To perform the surveys, a Global Navigation Satellite System (GNSS) antenna (Septentrio receiver) was mounted on the side of the boat on a pole directly above the depth sounder. This GNSS antenna recorded observations of elevation continuously at 1 Hz on all field days. These data were post-processed using precise point positioning (PPP) and converted to water surface elevation by subtracting the height of the antenna above the water surface when it was mounted on the boat to provide an estimate of water surface elevation.The data are limited to times when the boat was moving slowly enough such that its speed didn't affect the height of the antenna above the water. The data are provided in comma-separated values (CSV) format.