We have a flood-stage river in the middle of winter, and no purpose-made equipment. I'm in Idaho, so I'm going to assume conditions similar to those we have here. I'll figure air temps in the 30's, water temps also in the 30's. Swimming in swiftwater is much more challenging than most people realize. You don't simply swim across. Currents will move you downstream very quickly, and the current is much swifter in the middle of the river than along the banks. The current tends to push you toward the middle of the river, away from either side. Punching into an eddy when you're swimming is tough, even with proper equipment and flotation. It's even harder in cold water - it saps your strength very quickly, even with a wetsuit. The water is also cold enough that you would die from hypothermia very quickly even if you did successfully swim across. Swimming is out of the picture completely.

However, given the proposed scenario, it seems reasonable that you originally waded through the river to reach THIS side. So the normal depth of the river would be 1-2 feet, and not much more than 10-15 ft across - or what the heck were you doing walking across this river the first time? This means there should be trees growing out to the previous banks of the river from either side. I see one possible option to cross this river without getting wet. I carry a small saw in my PSK. I'd start downing trees along the current banks, which would rapidly get tangled up in other growth. If I cut down enough trees, I may be lucky enough to get a few tangled across the river in such a way that it's stable enough to walk/crawl across.

The downsides to this option that I see: risk of falling in - hypothermia, entrapment, death. Risk that a large piece of debris comes through, and shatters the 'bridge' and potentially me - wasted time, serious injury, death. Time consuming, I'll be clear-cutting the bank for hours, potentially days. Whatever is forcing me to cross this river is unlikely to take THAT long.

Even though this option seems to have a chance at getting me across the river alive, can't think of any possible situation in which this would be an effective option for crossing the river, and in which waiting until the river subsides is not an option.

For those suggesting using an upstream angle to ferry yourself across: dream on. Michael Phelps in 50+ degree water, maybe. Average person, no. In serious water, you're either swimming hard for the nearest shore, or trying to survive obstacles. If you try to maintain an upstream ferry angle, all you accomplish is to slow your cross-river speed. Your few miles an hour of upstream velocity are negated by far by the speed of the water carrying you downstream. The loss of cross-river speed from trying to maintain a ferry angle means the force of the current pushing you back toward the center of the river will overwhelm you. You'll be swimming as hard as you can upstream, and all you're accomplishing is wearing yourself out. Ferrying works much better for boats than it does for swimmers.