From OpenStreetMap Wiki
WikiProject Waterways aims to map the world's lakes, canals, rivers and other Waterways.
- WikiProject France/Cours d'eau
- WikiProject Germany/Gewässer
- WikiProject Poland/Rzeki
- WikiProject Hungary/Vízi út
- United Kingdom waterways
- WikiProject Belarus/Rivers
Tags for mapping waterways
Wikipedia has a river project, too: Wikipedia:WikiProject_Rivers.
wikidata project is here: wikidata:WikiProject_Rivers