Hi Lola
If the lone swan is not entering the pond, he is scared of the dominant swan. This means that he is not eating, bathing, or drinking. Eventually, he will get stressed and sick. Do you have someone in the area that has swans, is a swan/wildlife rehabber? The swan needs to be relocated to a better home without predators? Where are you located? If you can give us more info, please do so at Bolin.S@att.net and we may be able to find someone to take the swan. Unfortunately, since you have a mating pair, this issue is going to be a recurring one every year as the cygnets will be chased from the pond. The Regal Swan