The river that defines much of the border between the United States and Mexico is the Rio Grande. Stretching approximately 1,896 miles, the Rio Grande flows from Colorado to the Gulf of Mexico, creating a natural boundary between the two nations. Historically, it has been significant for trade, agriculture, and migration. The river is also crucial for local ecosystems and communities that rely on its waters for irrigation and drinking supply. However, it has been a contentious area in modern times, particularly concerning immigration and border security.