In 1988, the Center for Operational Oceanographic Products and Services (CO-OPS), an office of NOAA’s National Ocean Service, began to record continuous 6-minute water temperature data with thermistors at the coastal stations of the National Water Level Observation Network. Today, 140 of the stations have accumulated at least 15 years of archived data. We performed extensive quality control of the daily-averaged water temperatures by excluding periods of suspect data revealed through inter-station comparison. All quality-controlled series have 15-25 years of daily means that, when aggregated, produce an average seasonal cycle for 365 days of the year. Residual temperature series obtained after subtracting the average seasonal cycle from the daily mean temperature depict the inter-annual variations. A threshold for defining an extreme residual water temperature was selected to highlight periods of anomalously warm or cold coastal water conditions. This type of climate information should prove valuable to users in the fields of ecology and fisheries management for quantifying anomalous temperature effects on coastal ecosystems (such as fisheries, corals, sea grasses, harmful algal blooms, etc). Knowledge of average seasonal water temperature cycles are also useful for validating coastal hydrodynamic models. Extended periods from weeks to months of high or low coastal sea levels can be correlated with coastal water temperature anomalies.