I made a river for my club games (it's 6' long and 8" wide overall, but the actual water part is 6" wide) with a gentle meander. It's in 2' sections (and I'm in the process of adding some new bits (river bends, lagoon, and delta).
While the river itself counts as difficult terrain, each 2' section has a ford (wide enough for a land raider to use) that counts as clear terrain - or a bridge (wide enough for a baneblade).
Several armies hate it (non
IG or skimmer - but I have eldar and
DH/
IG as well as
SM and my
SM vehicles that can have them have dozers) but it does make for tighter games. As more often than not they are fighting over the bridge.