This is perfectly normal behavior. The swans are getting older and are of the age that the parents are trying to get them to leave the habitat. The more chasing and harassment, the greater the probability that the young swans will leave the area for either migration or to find another habitat and eventual life-time mate.

It is almost nesting time again, and the parents will chase the first brood from the area so that the new brood will have the food, nesting and shelter resources without competition from the older swans. The other swans are probably scouting the area to find another habitat and will eventually leave with the remaining swans. This is part of nature and how young swans are removed from the parent's habitat and forced to find their own space and mate. The Regal Swan