This dataset provides grain size distribution measurements collected from sediment core samples on Mike Island in the Wax Lake Delta, Louisiana, as part of the Delta-X Spring campaign in March, 2021,and the Fall campaign during August, 2021. The data are for March 26 and 29, and August 18 and 24. Sediment cores were collected using a piston core, then volume-based grain size distribution for each sample was measured using a laser diffraction particle size analyzer. The data are provided in comma separated values (CSV) format.