I foresee complications fording a river with a bike.

rules of thumb fording rivers:

wading staff held upstream- heavier current, use a heavier log. like, a big one - the size of your leg and 8 feet long!, to help break the current and weight you down as you lean on it. upstream.

don't tie yourself to any rope on shore...wrap it around the staff or your hand, but don't tie it onto yourself- that's a good way to get held under once you loose your footing.

I haven't tried it, but wonder if rolltop ortliebs would offer enough flotation for a loaded bike to be floated across?

alternately, Sevlor makes a very lightweight nylon backpackers raft designed specifically to ford rivers and cross lakes, etc.