The Rio Grande is one of the longest rivers in North America. It begins high in the mountains of Colorado, where melting snow runs into it. From there it flows south through New Mexico. Then it turns southeast and forms the border between Texas and Mexico for more than a thousand miles, until it reaches the Gulf near Brownsville.

In Mexico, people call the same river the Río Bravo. For thousands of years, people have used its water to drink, to grow crops, and to raise animals. Today, cities and farms on both sides of the border still depend on it. In very dry years, the water in some parts of the river gets very low, and people must be careful about how much they use.