The top layer of a breakwater consists of so called 'Armor Rock'. The part above water, which is visible, needs to have a nice, aesthetical slope. To achieve this, the rocks have to be placed one by one, just like a puzzle. The excavator operator searches for every spot the best possible stone. After placing the stone, he pushes and knockes the stones with the bucket to achieve a flat suface.
I have to say that some of these operators are real artists. If you see the stones on the stockpile, you cannot imagine that you can create a flat surface with it.