LLLL
xxFWWFxx
xxFWWFxx
xxFWWFxx
xxFWWFxx
LLLL
Each character resembles a space. For the best-looking results, I'd leave two spaces of straight river ("X") before having it bend. "F" is for placing the fences, "W" is the walkway, and "L" is the land. You could also make this bridge run East-West, though again, you'll won't have the illusion of water running under it.