This is the bike crossing at Nine Mile Creek in the southern suburbs of Minneapolis. Spanning the creek are two ropes which run through eyelets on either side of the raft, thus keeping it in its *lane*. There is also a rope attached to the raft and which runs to both side of the creek. When a rider comes down the steps on the far side of the creek in the photo, they use the rope to pull the raft over, then use it to pull the loaded raft to the near side.
And that is more or less how one got one’s Conestoga wagon across a deep river in the days before bridges.