Im not sure of the water quality, but Ive many a time have had to wade across it when it was at full flood. I think it was at at a game at sasco, when someone got his suburban stuck where the river runs over the road, and we spent about two hours of collecting gravel out of the running water to put under his mud dregded tires. It was real hot, and after we finally got it out, we had no energy and were totally soaked anyway, so we just decided to lay and rest in the cool water. Also on that same day, most everyone else who stopped at the flooded portion decided to just park and wade across on foot and get a ride from someone else. Plus, I think two other people got thir trucks stuck in the water, and spent a good half. an hour getting them out. Im sure that if the river were that polluted, than it would have had ill effects on any one of us. But Im certain that there are no diseases in the areas surrounding the river that far north of nogales.