A young swan is being stopped from going into the water by his parents and is living on the beach could this make him vulnerable to being attacked by foes or dogs
Strange, a swan not being allowed on water by its parents!
If the parents are being so protective, my guess, and it is only a guess, foes may have more to fear from the adult, adult swans can give a very nasty bite, but I'm no expert, so hopefully someone may be able to give a more definitive answer.
Maybe the adult Swans are trying to get junior to leave home thinking it was time it was independent while they prepare for the next breeding season.