I’ve been to Big Bend National Park, and soaked my feet in the Rio Grand. (Up to my ankles, as there wasn’t any water in the river then).
Back in Spring, 1983, we canoed the Rio Grande thru Big Bend, starting with Mariscal Canyon and ending at the Park HQ at Boquillas -- about a 4-day 45 mile trip.
First night out, we camped at the bottom of Mariscal -- at the base of sheer 1200 ft cliffs.
Aside from a couple of Mexican children fishing below one of the rapids on Day 3, we didn't see another human being for four days.
Absolutely one of the most remarkable trips I've ever experienced.