We would be guessing that this a pair of young juveniles (recently paired) chased from an area by adult swans and they are trying to make a habitat of their own. Your preserve probably looks very enticing with vegetation, shelter and food. Since the swans are protected in your country, we do not know if there may be a legal problem with trying to obstruct the wild swans. Therefore, we would suggest that you contact Wendy Hermon, Swan Lifeline Rescue Facility in Eton. She may be able to advise you on possible solutions to include the possible relocation of the swans to another area. The Regal Swan