In 2021, the TEPAST monitoring site was established to monitor the coastal conditions on the southeastern coast of Java, Indonesia. Six key variables - pH, temperature, chlorophyll-a, salinity, dissolved oxygen, and water transparency - are measured monthly using advanced scientific instruments. Over 36 months of measurements, 1488 samples were collected. The measured parameters were validated through monthly calibrations and statistical checks, with the distribution of each parameter assessed using histograms of the sampling data. Sampling at the TEPAST study site is conducted monthly, typically between the 15th and 20th of each month, from 7:00 to 10:00 local time (UTC+7). Morning hours are chosen to take advantage of generally calm water conditions, minimizing the influence of wind and waves on the data collection process. The TEPAST COD dataset includes two types of observations: (1) in-situ measurements obtained from three fixed locations over 36 months (September 2021 to August 2024) with measurements continuing, and (2) laboratory analysis of water samples to determine salinity and chlorophyll-a concentrations. In-situ measurements are performed at three depth layers: surface (0 m), 10 m, and 20 m. All instruments adhere to standard measurement protocols and are regularly recalibrated before use. The same individual conducted all measurements throughout the study to ensure consistency and minimize uncertainties. Seawater samples (1.5 L) were collected from each station and specific depth layer using a 3 L Nansen bottle for Chlorophyll-a analysis. The samples were immediately placed in cold storage on the boat and transferred to a dark -20°C freezer at the laboratory within one hour of collection.