Hi Michelle:
Are you sure that the swan is not looking at its reflection and either trying to chase the “new” swan from the area or trying to mate with it? We have seen this behavior in swans and other birds. Does he have a mate? If so, then he is trying to chase the other swan from his habitat. We would call this defensive behavior, not aggressive. In any case, he is acting like a normal male swan when the testosterone levels increase during mating season. The levels will decrease in the next few weeks, but until that time, you need to take back the habitat as the ALPHA swan.

The next time he chases or comes at you, DO NOT BACK DOWN. Without getting hit or hurt, once he starts to take a swing, grab his wings or throw a large blanket or towel over him while shouting NO. You may need your husband to help with this so both of you grab his wings, gently without hurting him. Hold him and place him in a garage, the bathroom, a shed, barn, or any area in which he is safely contained and cannot hurt himself or be attacked by a predator (domestic, (dog or cat) or wild). Keep him contained for about 30 minutes. Give him water, talk to him, tell him that this is not a good swan, hold his neck and wings, he will settle down. Then, release him back onto the lake. If he comes back at you, repeat the process. It will only take 2-3 times of this capture and letting him know that this is unacceptable behavior. If he was hand raised, he is not going to be too stressed by being captured, but he is not going to particularly like this new “time out” process. He will get the picture real quick that if he wants to go onto the lake, he is not to come out of the water and chase you. Otherwise, there are negative consequences to his bad behavior. Let us know how your training and re-taking of the habitat progresses. The Regal Swan