This reminds me of a criticism I once got when I first moved to London.
I tended to give preference to English words of clear Latin origin (e.g. such as 'construct' or 'respond', instead of 'build' or 'answer'), which was interpreted by this person as me attempting to sound pretentious, when in fact it was just due to my poor command of the English language. I was using the words most familiar to me. It probably sounded comical to hear such words being used along with poor grammar.
Had I been a sailor back then, I would have most definitely "navigated" rivers and seas, not 'sailed' them.
I guess you could separate them as 'Creeks' and 'Rivers', but the dimensions of a creek aren't really appropriate for a Civ game.
'Navigable River' is clear and no different than 'Impassable