Fun fact: the reversing falls in Saint John, New Brunswick (canada) are a place where the tides change the direction of the saint john river twice a day. In high tides, ocean salt water pushes into the river system and on low tides the river drains fresh water into the ocean. This is part of the bay of fundy which, due to a resonance effect, has the highest tides in the world. Tom scott did a video link below.

https://www.youtube.com/watch?v=nCrTsWtPVIY