Messages

The main thing is more contrast, highlighting, all waterways.
Changing colour in basemap is not necessary, i think most people are ok with it, so a selectable option, if it is possible to have a rather solid (not very transparant) outline to waterways in order to make waterways stand out a little more.

Maybe have a survey or brainstorm for river users or other water related options.

-a selectable more contrasting outline or darker blue, like emphasising roads would be my priority
-direction of flow, like in your screenshots would also be nice

Optionally:
-possible enter and exit points for canoing, danger zones, rapids, shallow zones, waterfall, hydro powerstations, wind shelters like in Sweden Vindskydd (i have these as personal POI for hiking and canoeing), other
-estimate lines for high and low tides?
-...

Maybe there are other requests from different water users, i believe this could be well appreciated extra selectable options.

Jef