Laboratory-based optical measurements for surface waters of the Upper Colorado River Basin collected during synoptic raft trips

This data release contains optical measurements for surface water samples collected during synoptic raft trips during three different sampling events. Data collection was performed by the University of Colorado at Boulder, Colorado (CO), and the U.S. Geological Survey (USGS) in Lakewood, CO. The raft was steered in the center of the river thalweg, generally between Kremmling, Colorado and Moab, Utah and discrete samples were collected at defined locations using a peristaltic pump. The surveys were conducted during the day, beginning in the morning and ending in the early evening. Sampling campaigns were conducted during high flow conditions from June 5 - 21, 2023, and May 15 - June 3, 2024. Sampling campaigns during low flow conditions were conducted October 3 - 19, 2023. The sample collection and laboratory analyses were performed through a joint effort of the Next Generation Water Observing System (NGWOS) and the Proxies Project (USGS Water Resources Mission Area, 2023) in coordination with the Colorado Water Science and California Water Science Centers. The optical measurements reported here were collected to establish proxies or surrogates for per- and poly-fluorinated alkyl substances (PFAS) and a suite of 12 elements of concern (EoC) as reported in Baesman and others (2026). The analyses were conducted by the USGS Organic Matter Research Laboratory (OMRL) in Sacramento, California (CA) including absorbance and fluorescence spectra and summary files to support statistical analyses.