It is the end of migratory season and the swans are returning to their nesting sites. They may be using the coastline to return to the nesting sites and will use the water to cool down before moving on. There may also be some brackish/fresh water estuaries that they can feed.

There is only one species of swan, South American Black-Necked Swans which can filter salt water so the Northern Hemisphere swans you are seeing will not stay in the saltwater for too long.

The severe weather that you have been having may also be a factor in the swans being forced near the coastline. The rain will provide them with the freshwater that they need if they are not able to immediately proceed to their nesting sites. The Regal Swan