This is a useful resource for running adventures by rivers and wetlands in general. It's basically well organized info from wikipedia with a few ideas on how they could be incorporated deeper into your games. You could do this yourself easily enough but it's nice that this is all in one place at least.

Marshes, swamps, fens, and bogs are not the same thing I had thought. Each has associated animals, plants and things assossiated with them. Great change of pace for tormenting your characters.