As part of the Triangle Area Water Supply Monitoring Project, the U.S. Geological Survey conducted a study to evaluate the occurrence and distribution of phytoplankton, taste-and-odor compounds, and cyanotoxin occurrence in four water-supply reservoirs in the Triangle area of North Carolina. This data release contains the associated data described in the Scientific Investigations Report, "Phytoplankton, Taste-and-Odor Compounds, and Cyanotoxin Occurrence in Drinking Water Supply Reservoirs in the Triangle Area of North Carolina". Surface-water samples were collected four times between April and October 2014 at five study sites for laboratory analysis of nutrients, chlorophyll a, major ions, metals, taste and odor compounds, and cyanotoxins for each sample. Field measurements of dissolved oxygen, pH, water temperature, and specific conductance were also conducted at the sites. This data release contains blank sample results, environmental data, replicate sample results, and phytoplankton results. The quality-assurance blank sample dataset contains the analytical results for the blank samples collected during the 2014 study period. The environmental dataset contains surface-water results for phytoplankton, taste-and-odor compounds, and cyanotoxin occurrence. The replicate sample dataset contains the analytical results for the environmental samples paired with their respective replicate collected during the 2014 study period. The phytoplankton dataset contains the analytical results for the phytoplankton data. The remaining field measurement data and chemical constituent results are available from Cain and others (2017).