How did shifts in the Rio Grande's channel lead to the El Chamizal dispute?

The El Chamizal dispute arose because the Rio Grande is a dynamic river prone to erosion, silting, and shifting its course. In 1864, a significant shift in the river's channel moved the boundary, effectively transferring the El Chamizal area—located between El Paso and Juárez—to the north (left) bank of the river.1

This geographic change created a long-standing territorial disagreement, as the river’s movement altered the established international boundary between the United States and Mexico. The dispute was finally resolved in October 1967, when the United States formally returned the El Chamizal tract to Mexico.1