Geometry: HydroRIVERS (© HydroSHEDS) — European rivers with at least 500 km² of upstream catchment; flow direction comes from the network itself. Names: canonical English labels from provider metadata and Natural Earth, with local-language aliases retained for search. Discharge: official national hydrology providers (latest available discharge; the measurement type is shown in each station panel), measured where a gauge sits on the river, otherwise estimated from drainage area and nearby gauges. Estimates are drawn dimmer; unsupported areas remain unknown. "Historical Comparison" classes each gauge's flow against its day-of-year percentiles when at least ten years of reusable observations are available. Every station panel identifies its provider, observation date, quality and official source.