|The picture came from here|
It has two arms that has a tub which fills with water. The tubs are filled accorcding to the Archimedes' Law. That means the tubs are balanced. Boats enter the tub and then the rotation begins. The rotation takes about 15 minutes to complete. Imagine all the planning that it took to put this kind of wheel together. I found a video on Youtube that I thought would help give a visual for it.
What a great way to see Scotland! Anyone up to a boat ride?