The Gila River (; O'odham [Pima]: Keli Akimel or simply Akimel, Quechan: Haa Si'il) is a  tributary of the Colorado River flowing through New Mexico and Arizona in the United States. The river drains an arid watershed of nearly that lies mainly within the U.S. but also extends into northern Sonora, Mexico. Indigenous peoples have lived along the river for at least 2,000 years, establishing complex agricultural societies before European exploration of the region began in the 16th century. However, Euro-Americans did not permanently settle the Gila River watershed until the mid-19th century.