This behavior does need to stop immediately to prevent him from getting run over. He is probably looking for a freshwater pond and Mute swans do not do well in saltwater. They cannot filter the salt and are truly freshwater birds. You need to see if you can find a wildlife rehabilitator in your area that may be able to capture him and take him to another fresh water area with other swans. We know that the Boston area is famous for their swans and this bird may have been separated from the downtown flock. We will call you as a follow-up. The Regal Swan