The river that forms part of the border between the U.S. and Mexico is the Rio Grande. This river flows from Colorado through New Mexico and forms a natural boundary between the two countries for a significant stretch. The Rio Grande is essential for both nations, serving as a critical waterway for agriculture, recreation, and ecosystems. It also carries historical significance as it has been a focal point of border policies and cultural exchanges between the U.S. and Mexico. The river is vital for many communities along its banks.