For a DnD 3.5 campaign I am hoping to run I need a variety of terrain features, with mountains / hills both sides of the continent, but also a very large marsh at one end.

I assume to have a marsh form you need a slow running river to split up and stagnate, what I am not sure is what natural effects differ to decide if you end up with a river delta, a marsh or floodplanes?

Also does anybody know of any real life marsh land I can check out for inspiration?