Only the Black Necked Swans of South America have the ability to filter salt from the water. Other species of swans can't, but can survive for short periods of time in salt water. The salt can cause them to be dehydrated so any large time spent could be detrimental to the swans. The major reason that the swans are in the ocean is because of the severe winter you have had and many waterways are frozen. Any water, especially on the way back from migration will be a welcome relief. Once the weather clears and warming begins, the swans will move inland for freshwater. The Regal Swan