Water quality observations made over long time periods can provide important feedback to scientists and to local, state, and national resource managers about actions taken to manage, protect, and restore estuaries. They also provide valuable information for evaluating the impacts of environmental change on coastal habitats and species. There are at least four water quality stations at each National Estuarine Research Reserve. Each station is designed to characterize long-term variability and short term changes in environmental conditions. Discrete samples for nutrient and chlorophyll a concentrations are collected at each long-term monitoring station at least once monthly. More intensive (24-hours over a complete tidal cycle) sampling is conducted each month at one water quality monitoring station to better understand impacts of tide and irradiance on nutrient cycling. Nutrient parameters collected include: nitrate, nitrite, ammonium, orthophosphate, and chlorophyll a. Numerous optional parameters include dissolved organic carbon, total dissolved nitrogen, and total dissolved phosphorous. The National Estuarine Research Reserves is a network of 30 reserves protected for long-term research, ecosystem monitoring, education, and coastal stewardship. Established by the Coastal Zone Management Act, the reserve system is a partnership program between NOAA and the coastal states. NOAA provides funding, national guidance, and technical assistance. Each reserve is managed on daily basis by a lead state agency or university with input from local partners. These data are collected as part of the NERRS System-Wide Monitoring Program (SWMP), which includes (1) abiotic indicators of water quality and weather; (2) biological monitoring; and (3) watershed, habitat, and land use mapping. Data were collected under individual Reserve NOAA grant/cooperative agreements and managed by the CDMO under NOAA grant/cooperative agreement #NA24NOSX420C0061-T1-01 (2024) and prior grants. For more information on Reserve locations and programs, please visit www.nerrsdata.org or https://coast.noaa.gov/nerrs/.