OK. This is cool. I don't want to fill my blog with ads for other people's stuff, but this I do like.
Hotz Mats just released a felt river system in a variety of sizes (1.5", 2", 3" and 4" widths). According to TGN's article, they come in a variety of lengths and can be customized if you need.
I love making terrain, but for smaller 6mm and 15mm games, these ready-made items that dont cost an arm and a leg just cannot be beat. Check them out!