Surface water quality, water isotope, and phytoplankton enumeration data were collected to evaluate the impact of an Emergency Drought Barrier (EDB) in False River in the Sacramento-San Joaquin Delta. Data were collected on six days during 2022 and 2023 (June 7, June 21, July 27, August 9, October 12, November 30, 2022, and February 21, 2023). Sampling occurred in Franks Tract, Mildred Island, the San Joaquin River, and various sloughs and cuts connecting these water bodies. High-resolution boat-based mapping data and discrete water samples were collected and analyzed for: nitrate, nitrite, ammonium, soluble reactive phosphorus (orthophosphate), total dissolved nitrogen, total dissolved phosphorus, total phosphorus, total particulate carbon and nitrogen, water isotopes (2H and 18O), dissolved organic carbon, chlorophyll a, and phytoplankton enumeration (microscopy).