This dataset contains annual oceanographic observations collected at the Helgoland underwater observatory (54°11.594′ N, 07°52.762′ E; WGS84) from 2013 onwards. Measurements include water temperature, salinity, oxygen saturation, chlorophyll-a concentration, and turbidity. The observatory is located at a water depth of approximately 10 m (± tidal variation) and is equipped with one or more sensors for each measured parameter. Observations are recorded at an hourly temporal resolution. All data have undergone quality control using the four-step plausibility and quality assurance procedure described by Waldmann et al. (2022). The cabled observatory infrastructure and sensor configuration are described in detail on the AWI COSYNA underwater observatory webpage. For comprehensive information on instrumentation, sensor deployment, calibration procedures, and data processing, please refer to the annual metadata documents entitled metadata_heluwobs_yyyy_hydrography.pdf associated with each yearly dataset.