Cygnets cry constantly looking for mother. You are now its mother, so just touch him and speak to him so that he knows you are nearby. The crying sounding more like a meep meep is the cygnet's and nature's way of telling the mother where he is located. So, this is normal behavior.

He may be in some distress due to the hobbles, but again, this will work itself out and is for the benefit of his future leg usage. Hobbles, when used quickly at the early diagnosis of "splayed" legs can work, surgery is not that successful, so it seems that he is at least on a good path forward for healing.

As far as water, you do need to dunk or spray him so that he learns to preen and keeps the uropygial oil gland working and the feathers healthy. You can prevent the hobbles from getting wet by just spraying his feathers with a water bottle or dunking just his body and then drying him so that he is not dripping. Then, he will learn to dry himself by using the oil gland. The Regal Swan