We're being a little sloppy with terms here. "Inland" started out referring to swamps near the center of a continent ... far, far away from any coast ... while "coastal" started out referring to swamps 'near the coast' ... which I took to imply within a hundred miles of the coast or thereabouts. Now we are splitting hairs over brackish waters or not.

Most swamps in Florida are freshwater, except for those directly connected with the Gulf of Mexico or other tidal water body. Minnesota is 100% fresh water swamps.