I've seen few swamp maps, and those I have, are always alike. This one looks quite different and is looking very good. I'm eager to see its scale and ho you throw the rest of the details in.

The green areas looks nicely marshy and I like that ss greener at the center. I see the rivers very wide, specially at the "entry" point, but that may be a matter of scale or simply that's the way it is. I don't have much experience on marshes.

Anyways, great start!