I've heard that a swan can break your arms with a flap of its wings, etc., but am not sure if that's true. There's a nature reserve - local to me - where the swans come up on foot out of the water and approach humans voluntarily, obviously looking for food. I've been feeding them (with appropriate things, not white bread) including holding out food in my hand for them to take.
Is this safe or have I just been lucky so far? - I was a bit intimidated as they seemed quite pushy asking for food once they knew I had it (I'm 5'5 and they come up to chest height to me!) and I didn't know how to respond!