Steve, Chris and I wanted to add some water to our African adventures, so I made two rivers. One is 6 inches wide and the other is 12 inches wide. Both are about 6 feet long.
I just used some cloth and painted it with fabric paint. Painting water was a lot more difficult than I thought and I spent a lot of time trying to make the water look realistic. The final product isn't great but should be good enough for some gaming.
Of course, I couldn't leave my natives stranded on the shore so I made a bunch of canoes out of balsa wood.