The Rio Grande is 1,896 miles long; of that total length, 1,250 miles of it is in the state of Texas, forming some of the border between Texas and Mexico. It has a tributary, the Pecos River. Adventurous outdoorsmen have long enjoyed camping along the Rio Grande, particularly in the scenic environs of Big Bend National Park. Here, you can enjoy such activities as hiking through the desert or along the river's bends, or whitewater rafting in the river itself.
The Red River is a tributary that flows into the Mississippi. Of its total length of 1,360 miles, 680 miles of it is located in Texas, forming part of the border between that state and Oklahoma. The Red River is optimal for canoeing and paddling, as it is a wide river with flows of between 5,000 and 10,000 cfs, and the water is clear and unpolluted. Whitewater rafters won't find much to appeal to them in the Red River; given the calm flow, it is best navigated by canoe or paddle boat. Keep in mind that there are no public or private campsites along the river in Texas, though you shouldn't have a problem improvising a campsite somewhere along the river. The land surrounding the Red is mostly flat, empty and undeveloped, so it is perhaps not the most fascinating territory for hikers.
While the Brazos River has the third largest total length (1,280 miles) of any river flowing through Texas, it has the second longest section of river within Texas itself (840 miles.) It is also one of the cleanest rivers in the state of Texas. The river runs through the Palo Pinto Mountains, providing scenic views to hikers and boaters alike. Like those who plan on traversing the Red River, be prepared to improvise when it comes to camping out. The Brazos is perhaps best undertaken by canoe or paddle boat; there are, however, Class II - Class III rapids near the Highway 4 crossing. Otherwise, it should be a smooth journey.