how do ships travel up and down rivers with different water levels

It's actually pretty simple once you get the hang of it, but it catches a lot of people off guard. To figure out which is which, you have to imagine yourself standing in the middle of the river, facing the same direction the water is flowing—basically, looking downstream toward the sea or the end of the river. Everything on your right hand side is the right bank, and everything on your left is the left bank.

I deal with this all the time when I'm out on the water. It’s super important to keep it straight because if you're navigating or just trying to explain where you're anchored, mixing them up causes a total mess. You'd be surprised how many folks try to guess it based on which way they are looking while standing on the shore, but that just doesn't work since the orientation flips depending on where you're standing. Just remember to always orient yourself with the current and you'll be golden.