Mexico Declares U.S. State Cannot Alter International Border over Nine Islands

Mexico’s Foreign Ministry made a firm statement on Friday, October 31, 2026, that the border shared with the United States cannot be changed by a state‑level government. The message was directed toward the claim made by Texas’ General Land Office, led by Commissioner Dawn Buckingham, that nine islands in the Rio Grande—known in Mexico as the Rio Bravo—belong to the state of Texas. This position was at odds with Mexico’s longstanding position that the international boundary is fixed by treaties and international bodies.

According to the ministry’s statement, the 1970 Mexico‑U.S. Boundary Treaty remains the legal framework governing the border along the Rio Grande. The treaty establishes that the boundary follows the centre line of the normal channel of the river, and that line determines sovereignty of the land on either side regardless of prior ownership. This definition applies to all land features within the river, including the islands under dispute.

Central to the dispute is the role of the International Boundary and Water Commission, the joint body authorised by the two governments to implement the treaty. The commission has the authority to decide on which side of the boundary each island lies. The ministry emphasized that no state‑level government—whether in the United States or in Mexico—has the power to make such determinations independently of the commission.

In addition to defining sovereignty, the treaty places limits on what kind of work can be undertaken along the riverbanks or on the islands. The Ministry stressed that neither country is allowed to build structures that the International Boundary and Water Commission finds could alter, obstruct, or otherwise affect the normal flow of the river. The commission’s oversight is meant to prevent unilateral actions that could change the geography or hydrology of the boundary area.

The Ministry’s response comes after the Texas General Land Office declared the islands as property of Texas. That declaration was viewed as a unilateral move that disregards the treaty’s provisions and the commission’s responsibility. Mexico’s statement reinforced that sovereignty over the islands remains an international question, to be handled by the commission rather than a state authority.

Going forward, Mexico said it would closely monitor any actions taken in the area. The Ministry reaffirmed its commitment to abide by the treaty and to pursue dialogue through established mechanisms. By making that commitment, Mexico signals its intent to keep the border unchanged and to preserve the peaceful resolution of the dispute through the established treaty process.

The Rio Grande has long been a symbol of the shared geography between the two countries, and changes to its course or to its islands have historically been handled through diplomatic channels. The 1970 treaty codifies the practices that have guided the two nations for decades, and Mexico’s stance reaffirms that the border’s status is not subject to state‑level claims but to the agreements that both nations have signed and renewed over time.

This statement and the surrounding context underline a broader principle that international boundaries, once defined by treaty, remain immutable without mutual agreement. As the dispute over the nine islands unfolds, both Mexico and the United States will likely rely on the International Boundary and Water Commission to maintain the regime that has governed the Rio Grande for over half a century. By reaffirming that the treaty remains in force, Mexico upholds the legal framework that ensures the border is managed, not changed, through diplomatic and institutional channels.