it depends what type of waterways you’re after.
for the sea, https://map.openseamap.org/ is very good (but no route planning sadly - for that you’d need opencpn and some charts obtained.
For inland waterways i can only speak for the English canals, for which i recommend https://opencanalmap.uk/ which uses data from both OSM and the Canal and River Trust. Again, sadly no route planning but for that I use https://canalplan.org.uk/
replyThe OSS tool for nautical charts is OpenCPN.
replyOsmAnd has a nautical map plugin you can enable.
replyThe plugin is just part of why OsmAnd is good for nautical use, there is also an alternate view in the configure map menu for nautical use.
replyFor some reason osmAnd was the only GPS map that would work on a flight for me.
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