If I understand you correctly, this would expose you to river water for a much longer time - an outcome not desireable in a winter scenario.

By tethering the downstream end of the pole / door in the right place, hopefully you ride the "closing door" pole to the place of your choice on the other side of the river - near your vehicle in my scenario - relatively quickly. And if you successfully rig a small float/ raft to ride across you may not expose your core to the water much if at all. Then into your waiting vehicle with its winter kit of change of clothes, food, heater, etcetera.