Background: High-resolution monitoring of rivers is important because rivers are severely affected by climate change and frequency/magnitude of extreme events are changing fast. Advanced in-situ monitoring technologies have to be combined with satellite earth observation (EO) to obtain accurate, reliable and spatio-temporally resolved information for effective decision support, risk assessment, climate change adaptation investment analysis, and operational forecasting/surveillance. Problem being addressed: Traditional hydrometric monitoring of rivers is in-situ and station-based. In-situ monitoring networks lack spatial resolution, have been declining in many regions, and data accessibility is increasingly restricted because of growing conflicts between countries over water resources allocation. In order to solve this problem, hydrometric monitoring using satellite earth observation has to be combined with drone-borne hydrometric monitoring technology for validation, deployment in remote and inaccessible regions, and to enable reliable and accurate river discharge estimation. Our solution: UAWOS develops a drone-borne water observation system providing key hydrometric variables (bathymetry, velocimetry, water surface elevation) at high spatial resolution/coverage, and data-based products/services supporting management and decision making. UAWOS integrates airborne data streams with Copernicus water bodies and water level services for cross validation and to estimate river discharge from satellite EO data. Impact: We expect that UAWOS hydrometric monitoring solutions will be factor 2-3 cheaper compared to traditional in-situ surveying. UAWOS technology will provide very high spatial resolution with accuracy on par with traditional in-situ monitoring. The technology will support smart governance/regulation in the context of the Green Deal, and create new opportunities for European business, both as a stand-alone solution and in combination with satellite EO.