If it's about the DC area, which is between Maryland and Virginia, here are links that list the swamps there.
Since "a swamp is a wetland that is forested", we might also need to use the word "wetlands" as a search term, I don't know.
https://www.neefusa.org/nature/land/wetlands-united-states#Maryland
https://www.neefusa.org/nature/land/wetlands-united-states#Virginia
https://en.wikipedia.org/wiki/Category:Swamps_of_Maryland
https://en.wikipedia.org/wiki/Category:Swamps_of_Virginia