Like TM7, I have canoed the Rio several times, and fished along the river in several places. The majority of the time the river is low enough that a short legged mexican can wade across and not get his hip pockets wet. But there area several areas where even a good swimmer can get in trouble in a hurry.
I made the trip several times from Lajitas to La Linda (look that one up on the map), even had lunch at the "Howard Johnson's" on the American side, (but only once). Back in the early eighties it became very dangerous to make the river trip. The Mexicans would shoot at rafters or conoes from the high peaks on the mexican side of the river. A local man and his wife were on the river with several other couples, he was shot and killed, she took a couple of hits, but survived. After that they discouraged river trips for several years, but it is a big business for several river tour groups today, and a good time and experience for those who wish to try it. If you are thinking of one of these trips, Thanksgiving to early Febuary is the best time, From about the end of May to November it is so hot (100 plus degrees) that it is very dangerous to even attempt a trip.