When I visited the place, the river seemed calm almost as a pond. I didn’t get in though because it seemed too dirty due to the drought. But getting across should not be problem for anyone with at least meager swimming skills. I suppose that on wider sections one should be always able to reach the bottom with his feet. Crossing on a horseback would definitely be completely no problem.
Well, for example if enemy soldiers are tracking you, going through river is a great way to lose them.
Or when you need to get into a guarded area, getting through water in the night is exceptional option.
Waterways were also used in the middle ages to transport anything large (downstream on its own, pulled by horses upstream). I see plenty of options how the river may be used, hopefully WH will