Mountains -> Swamp -> River Question

[seycyrus]

Greetings,

I've made and been using the attached player map for my group and realize I might have created an unrealistic topology. I have lurked long enough to have picked up on some of the rules of rivers, but realize I might have made a transgression.

In the map, the main river flows from North to South. My question is about mountain area in the southeast (fenced by the rivers). The greenish area (yes, I know there many greenish areas) around those mountains (fenced in by the rivers) is meant to be swamps or marshes. Is this realistic? Does this ever occur in the natural world? Does water ever flow off of mountains via a bunch of small streams etc. into a flat swamp area and THEN drain into a larger river?

Thanks for your help!

Oh yeah, other criticisms of the map are welcome as well. Yes, the castle is not to scale