There are only two things that can be done to solve this situation. Either build up the current area or try to entice them to another area which has higher ground. Unfortunately, swans and many other waterfowl will continue to return to the same nesting site because they are familiar with the habitat, its resources, predators and other attributes/problems with the area. Trying to entice them to another area may be the most challenging, so building up the present area for next nesting season may be the viable solution. The Regal Swan