There is still a possibility that the eggs are okay and the parents are just taking a rest from the nest. If they do not return to the nest to sit, then you can safely assume that the eggs were destroyed in the flood. The swans may or may not re-nest and lay more eggs this year. The later into the nesting season that something like this occurs, the less likely that they will have more eggs because the hormones start to go back to normal and are not at the level for mating/egg production/nesting. The Regal Swan