Wandering from the pond is a major concern as it leaves the swan open to predation or possibly being hit by a vehicle if there is a nearby road.

Now, having said this, if these are captive swans (cannot fly), then this is relatively normal behavior. The swan is migrating. Yes, non-flying captive swans still feel the urge to migrate and will try to wander southward. Usually, if you keep dissuading the swan from this behavior, i.e., someone constantly picking him up or chasing him back into the pond, this behavior will usually stop as the swan gets the idea that he is not going to be able to go anywhere. You definitely want him back in the pond prior to dusk as he will be attacked if there are predators in the area.

Secondly, male swans have the duty to protect the family. Once the cygnets are old enough to be on their own or primarily hang around the female, the male will start to wander around the pond and leave the nesting area. The young cygnet is probably a female as the male is still accepting her in the area and he does not see her as a male rival. So, he will leave the two females to themselves as he exercises some freedom.

If this were a male cygnet, the male would have already chased it from the area, thus causing stress to the cygnet. If this is the case, you might need to find another home for the cygnet to prevent any possible stress related injury or illness or subsequent fights.

You probably don't need to do anything except keep an eye on the swan and make sure he does not wander from the pond (20 feet is too far in the event a predator is chasing and he cannot get back into the pond quickly). Additionally, make sure that once he returns to the pond and normal behavior, he does not begin to chase the cygnet from the pond. Again, this would warrant finding the cygnet a good safe home elsewhere. The Regal Swan