Why not add some kind of flow to the rivers in H&H? I'm not sure if its possible to implement but ill never know if i don't ask.
When you look at rivers right now, its pretty dead. You stay at the same place if you stop traveling and you go at the same speed wherever you go.
Here are my main ideas regarding this.
-When you go WITH the current, your boat could be going at normal speed and your char would suffer no stamina lose.
-When you go AGAINST the current, your boat would go slower DEPENDING on the strength you put into rowing (rowing strenght could work like the run speed, each level being more demanding in stamina.).
-If you decide to not move at all, the flow would carry you to its end, wich could be a lake, sea etc.
Of course, if this affect the boat, it should be able to affect other things such as:
-People swimming
-Flotsams (imagine picking up a bear and see a flotsam going past you in the river

-Logs, would make it much easier than to pick them up with a boat.
For the people that want to remain at a same place in a river, they would use an anchor wich could be crafted with a rope and stone/metal.
As for how the current works, I said the river systems should work something like this.
Stream---\
Stream------River----\
||||||||||||||||| ------Lake/Sea
Stream------River----/
Stream---/
Well, that's all i think of right now
