Deliverable 3.1 summarizes the data availability, data sources and their spatiotemporal extent for the NAPSEA project basins draining into the Wadden Sea with a specific focus on the case sites Elbe, Rhine and Hunze. The data will be used to setup the water quantity and quality models in task 3.2 (mHM, mQM and CnANDY) to backcast concentrations and loads and capture spatial patterns of nutrients (Nitrogen and Phosphorus). These models will serve for testing the efficiency of different stakeholders-selected mitigations measures to ensure the safe ecological boundaries of both case studies. Data include climatic forcing, land use properties, soil type, point-sources (sewage stations and their discharge), agricultural practices (manure, mineral fertilizer) and measured stream discharge and nutrients (Nitrogen and Phosphorus) concentrations. Observed data covering the longest time series were prioritized in the analysis to ensure a good historical coverage of nutrient-pollution background conditions. Table 1 and table 2 summarize the spatiotemporal coverage of data availability and sources. The deliverable was planned as a “data collection” in the project proposal. This document lists and describe the data, their data source and enables access to the data. The minimum data to run the model is available in FAIR repositories and open access publications such that everyone within the project consortium but also outside can access the data.