The local game store carries a selection of items from Pegasus Hobbies. This particular piece is their Museum Models River Set.
You get about 4' of river. It is painted plastic. The water sculpting is a bit odd, but it still looks good and is a steal at $20.
We found that to enhance the look it helps to give the dirt colored banks a wash of Citadel Brown wash. It gives the bank more depth, and dulls the glossy finish. A bit of ground cover on the bank really enhances the look as well.
A ford was added to one of the short, straight sections to create a crossing for our Song of Blades and Heroes Campaing we will be running starting January.
My friend Brian simply coated a section of the river in white glue, then placed some stones randomly in the river. The result is a quick and effective method.
The glue is still wet in these pictures, but it does dry clear and looks good.