This river’s valley is home to the World Birding Center, a series of nine parks including ones in Roma and Harlingen. (15[1])It's not in Iraq, but Bagdad Beach lies just to the south of the mouth of this river. The Charro Days festival is held along both sides of this river. Shantytowns called colonias along this river pose public health problems due to lack of clean drinking water. In 2020, there was a large (*) GOP swing in Cameron and Starr counties in this river’s valley. This river is just south of SpaceX's Starbase and the vacation spot South Padre Island. Big Bend National Park is named for a section of this river, which divides the cities of Brownsville and Matamoros, and Laredo and Nuevo Laredo. For 10 points, name this river that establishes the eastern part of the US-Mexico border. ■END■