Are there any salt water swamps?

Yep! They are generally called marshes when they have saltwater. You can find tons of them all along the coast really. They usually have tall grass, and a bunch of channels of water zig zagging through. They are a very important habitat for crabs, birds, shellfish, fish, and other marine critters. The water levels also correspond to the tides as well, so low tide they can appear to be just mud, and high tide you see the channels.
Yes.
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A saltwater swamp or marsh is formed by the flooding and draining of seawater. Evidence of one would be the plant called the Mangrove, which can survive in conditions like so.



So yes, there are saltwater swamps.