Falkirk Wheel

https://www.youtube.com/watch?v=_tBH9SE-Kw8 tells us that the Archimedes principle (objects move an amount of water that correspond to their weight) is useful to equilibrate the two arms of the wheel in order to have correct balance.

edit: and that the amount of energy to do one rotation is just 1.5kWh (@22.5kW) ... incredible!

I saw the Falkirk Wheel last year and it's amazing. The design deliberately calls back to 19th century British engineering works like those of Brunel, Watt, and others. Well worth a visit if you are in Scotland.