In cooperation with the Texas Commission on Environmental Quality (TCEQ), the U.S. Geological Survey (USGS) utilized various field and laboratory methods to determine the presence and concentration of cyanobacteria, cyanotoxins, and taste-and-odor compounds in Texas water bodies. This data release documents the results from water-quality samples collected from 41 water bodies in Texas during 2016–19. Both qualitative and quantitative field and laboratory methods were performed. Analyses included phytoplankton taxonomy, measurements of phytoplankton biomass, and concentrations of cyanotoxins, taste-and-odor compounds, and photosynthetic pigments. Water-quality samples were also collected to provide supporting data and document existing conditions. These supporting data included dissolved solids, major ions, nutrients, and organic carbon. The study began in water year 2016 (WY16). A water year is defined as the 12-month period from October 1 through September 30 and is designated by the calendar year in which it ends. During water year 2016 and 2017, water-quality samples were analyzed for total and dissolved cyanotoxin concentrations (anatoxin, cylindrospermopsin, domoic acid, microcystin [total and 10 congeners], nodularin, okadaic acid, and saxitoxin), taste-and-odor compounds (methylisoborneol [MIB] and geosmin), chlorophyll a, pheophytin a, major ions (calcium, chloride, fluoride, magnesium, potassium, silica, sodium, and sulfate), and nutrients (nitrogen, phosphorous, and multiple species of each nutrient). In water year 2018 (WY18), analyses of cyanobacterial- and cyanotoxin gene concentrations were added to the study. In water year 2019 (WY19), the study design further expanded to include In-Situ Aqua TROLL sensors to compare the field values with the EXO2 multiparameter sonde. Each reservoir had one sampling site with the exception of three reservoirs at the beginning of WY2016. At those three reservoirs, only selected water-quality field properties were measured on site at 1-2 sampling sites —there were no water-quality samples collected at these sites. At all other sampling sites, water-quality field properties were measured every foot of the water column until the irradiance was 1 percent of the irradiance measured at the surface of the water column. Subsequently, water-quality field properties were measured every five feet to the bottom of the water column. Three rapid-assessment field kits were used to determine semi-quantitative values of three cyanotoxins (anatoxin, cylindrospermopsin, and microcystin) at each sampling site. Chlorophyll-a and pheophytin-a were analyzed by the Trinity River Authority Central Laboratory in Dallas, Texas. Cyanobacterial and cyanotoxin genes were analyzed by the USGS Ohio Water Microbiology Laboratory in Columbus, Ohio. The USGS Organic Geochemistry Research Laboratory in Lawrence, Kansas analyzed for cyanotoxins and taste-and-odor compounds. PhycoTech, Inc. determined phytoplankton taxonomy and biomass. Engineering Performance Solutions in Jacksonville, Florida analyzed for MIB and geosmin. Samples were analyzed for nutrients and major ions by the USGS National Water Quality Laboratory in Denver, Colorado. Water-quality field properties (water temperature, dissolved-oxygen concentration, pH, specific conductance, turbidity, chlorophyll density, chlorophyll fluorescence, phycocyanin density, phycocyanin fluorescence, irradiance, and Secchi depth) were also measured at each sampling site. Water-quality field properties and water-quality constituents are commonly referred to as “parameters” by analytical laboratories, and laboratory terminology for the datasets described in this data release were retained.