The five files contained in this compressed folder contain all water quality records downloaded from the Water Quality Portal on May 2nd, 2019. The five parameters are: Colored Dissolved Organic Matter (CDOM), Chlorophyll a (chlorophyll), Total Suspended Solids (TSS), Dissolved Organic Carbon (DOC), and Secchi Disk Depth (secchi). These data cover the continental united states and Alaska. These are raw outputs and just aggregated, all metadata are available here: https://www.waterqualitydata.us/.
This data was part of building the AquaSat dataset with a github repo here: https://github.com/GlobalHydrologyLab/watersat