This dataset provides in situ measurements of beam attenuation coefficient at 670 nm (m-1), average suspended particle size (um), particle size distribution (uL L-1), and water temperature (degrees C) in surface waters (~0.5 m) collected during the Delta-X Spring 2021 campaign. Measurements were made in the Atchafalaya and Terrebonne Basins on the southern coast of Louisiana from 2021-03-25 to 2021-04-22. During the field campaign, measurements were collected in multiple channels of varying width (from a few meters to >100m), near Delta-X intensive study sites, in open bays and lakes, and at a few locations in the nearshore Gulf of Mexico. For each in situ collection, the measurements were collected using Sequoia Scientific Laser In-Situ Scattering and Transmissometer instrument (LISST-200X).