Troubled Waters: Recent Challenges to the 1970 US-Mexico Boundary Treaty

In June 2023, Texas Gov. Greg Abbott deployed a string of huge buoys in the Rio Grande near Eagle Pass, Texas, ostensibly to deter migrants from crossing the river as part of his controversial Operation Lonestar (Garcia 2023). In so doing, he drew national attention to a little-known treaty setting the boundary between the United States and Mexico: the 1970 “Treaty to Resolve Pending Boundary Differences and to Maintain the Rio Grande and the Colorado Rivers as the International Boundary.”

This agreement — generally referred to as the U.S.-Mexico 1970 Boundary Treaty, or simply the 1970 Boundary Treaty — is now caught up in border security and immigration contention, something its architects probably never considered. Abbott’s controversial initiative to unilaterally insert state power into the administration of U.S. border security and immigration policy may well contravene several federal statutes governing immigration and navigation administration, and is now being challenged in federal court. It is clear, however, that Operation Lonestar violates provisions of the 1970 Boundary Treaty.

This paper reviews the origins of the 1970 Boundary Treaty, its key provisions, and challenges arising from U.S. border security and immigration measures since 2007. It also describes recent measures taken under the banner of Operation Lonestar and considers the merits of Texas’ actions and implications for bilateral relations. The paper concludes with observations on the treaty’s enduring value to both countries.

Origin and Development of the Treaty: A Capsule History

The international boundary separating the United States and Mexico was set by two treaties:

1. The Treaty of Guadalupe Hidalgo, which ended the Mexican-American War of 1846–48, fixed the boundary at the Rio Grande between El Paso, Texas, and Ciudad Juárez, Chihuahua, in the deepest channel of the river (Guadalupe Hidalgo 1848).
2. The Gadsden Treaty, by which the U.S. acquired 29,640 square miles (76,800 square kilometers) of land south of the Gila River in 1853, set the boundary east of the Colorado River some 24 miles south of the Gila River’s intersection with the Colorado River — establishing that stretch as a riparian boundary and maintaining that boundary in the deepest channel of the river (Gadsden Treaty 1853).

The 1970 Boundary Treaty has its origin in the riparian nature of these boundaries.

Riparian boundaries are inherently dynamic, continually altered by the ceaseless movement of water. Shortly after the boundary treaties were signed, it was evident that establishing each nation’s sovereign limits would be challenging. Small tracts of land were regularly swapped from one country to the other as spring floods caused the rivers to skip their banks, carving new riparian corridors. The problem was addressed by an 1884 convention that distinguished between routine erosion of the river banks and floods that carved new channels: It pledged to reset the river course in the event such surges occurred and altered the boundary (Convention 1884). Unfortunately, the agreement was not retroactive, nor was it effectively applied in its early years — even though a binational agency was established in 1889 to do just that. Thus, various instances of contested sovereignty accrued.

The largest of these tracts, known as El Chamizal, was located at El Paso, Texas, and Ciudad Juárez, Chihuahua. After a notorious effort to settle the Chamizal question by means of arbitration failed in 1911, Mexico refused to negotiate settlement of other detached tracts until the Chamizal dispute was resolved (Lamborn and Mumme 1988). A 52-year impasse resulted, despite earnest efforts by the Roosevelt, Truman, and Eisenhower administrations to settle the matter.

International Boundary and Water Commission Established

Despite the ongoing boundary dispute, in 1944 the two countries moved to consolidate boundary administration and transboundary water management in a new agency, the International Boundary and Water Commission, United States and Mexico (IBWC) (Water Utilization 1944).[1] With the ratification of the U.S.-Mexico Water Treaty in 1945, the new IBWC was endowed with exclusive authority to interpret and apply all boundary and water treaties in force between the two countries and assumed a leading role in boundary management. The intractable Chamizal dispute ensured, however, that the IBWC’s national sections would after 1945 work closely with their respective foreign ministries on settling the problem (Lamborn and Mumme 1988).

The Chamizal issue was finally laid to rest by the Kennedy and López Mateos administrations in 1963 using a formula that mirrored the ill-fated 1911 arbitral decision: The contested tract was divided and roughly two-thirds of the 700 acres were allocated to Mexico (Boundary 1963). This historic achievement paved the way for further negotiations on the disputed tracts, referred to as “bancos” in Spanish, and boundary stabilization that produced the 1970 Boundary Treaty — ratified in 1972.

Barriers, Impediments, and the Treaty

The 1970 Boundary Treaty encompasses key elements of early boundary agreements, including the 1848, 1853, and 1884 treaties, while also:

• Making provision for specific boundary adjustments.
• Clarifying sovereignty over any islands found in the watercourses.
• Further specifying each nation’s obligations to preserve the integrity of the boundary throughout its 1,954-mile reach.
• Setting the maritime boundary at either end of the land boundary, on the Gulf of Mexico and the Pacific Ocean (Treaty 1970).

Main Articles of the 1970 Treaty

As specified in Article I, boundary adjustments on the Rio Grande were made at the Horcon and Beaver Island tracts upstream of Hidalgo, Texas, and Reynosa, Tamaulipas, as well as at Presidio, Texas, and Ojinaga, Chihuahua.

Article II addresses the problem of sovereignty over riparian islands by placing the boundary in the center of that channel in which the river’s normal flow produces the greatest width over its length (Treaty 1970). More than 300 islands were assigned sovereignty under this provision (Rogers 1971, 676).

Article III, in effect, updates the 1884 Boundary Convention to provide that — in cases of gradual erosion — the boundary would float in the center of the river channel. However, where water surges separate a tract of land by carving a new channel it distinguishes between tracts smaller or greater than 250 hectares (Treaty 1970).

• When there is a separation of less than 250 hectares, the country from which the tract was separated is allowed to reset the river to its original location at its own expense within three years. If this is not done, the land passes to the receiving country with the river, and the boundary, remaining in its new location.
• With a separation larger than 250 hectares, the boundary must remain in its original location and the IBWC is to restore the river to its original location, or the two countries may rectify the river channel, restoring an equal amount of territory to the party from which the tract was separated — with costs in both cases shared by the two countries (Treaty 1970).

Article IV takes up the issue of works affecting river flows and the position of the boundary. This article is key to maintaining the boundary as a reliable demarcator of territorial sovereignty. As U.S. Secretary of State, William Rogers, put it in his letter to Congress advocating for the treaty’s ratification:

This article would obligate each government to prohibit the construction of works that would deflect or obstruct the flow of the river to the disadvantage of the other country, to remove or modify works that do cause damage, and repair or make compensation for any damage (Rogers 1971, 677).

Each country is permitted to construct works aimed at stabilizing the boundary rivers’ banks, provided they do not have an adverse effect on the other country or deflect the location of the boundary, both under the conditions of normal flows or flood events (Treaty 1970). The construction of works that the commission believes could deflect or obstruct the normal or flood flows of the main channel of a boundary river is prohibited — this prohibition also applies to a specific distance from the boundary (determined by the IBWC and agreed upon by the two governments) in the adjacent lands (Treaty 1970). If the commission determines that works constructed by one or another country could deflect or obstruct a river’s flows, that government must remove them or modify them at its own expense and, as determined by the commission, repair or compensate the other country for any damages incurred. The IBWC is also charged with recommending governmental approval of works it deems necessary for the stabilization of the boundary on the Rio Grande and Colorado Rivers. Works may include “clearing, channel excavations, bank protection, and rectifications” (Treaty 1970).

The 1970 Boundary Treaty also, for the first time, set the two countries’ nearshore maritime boundaries. Under the terms of Article V, the boundary in the Gulf of Mexico was set from the center of the river “wherever it may be located” (it changes with erosion) to a specified fixed point 2,000 feet off the coast and then in a straight line to the 12 nautical miles limit in the Gulf.[2] On the Pacific Ocean side, the line extends from the westernmost point on the mainland boundary in a series of straight lines to the 12 nautical miles limit (Treaty 1970).

Ratified in 1972, with its specified boundary rectifications completed by 1977, the treaty served the two countries remarkably well and without controversy until 2007. After that, U.S. border security measures authorized by the Secure Fence Act of 2006 began to intersect with boundary maintenance, as fence building aimed at deterring smuggling and unauthorized migration ramped up (White House 2006).

The following sections outline the boundary treaty’s important role in defining limits of subnational authority over the rivers and the boundary.

Boundary Maintenance and Border Security

As security measures — driven by mandates conferred on the Department of Homeland Security by the Real ID Act of 2005 and the Border Fence Act of 2006 — increased along the boundary with Mexico after 9/11, it seemed inevitable that the 1970 Boundary Treaty would be tested (Nuñez-Neto and Garcia 2007). Unilateral barrier construction along the boundary was vigorously opposed by Mexico (Nuñez-Neto and Garcia 2007, 31). Along the Rio Grande, treaty-related concerns arose as early as 2008, when proposals surfaced to accommodate Department of Homeland Security (DHS) fence building plans by placing concrete barriers atop existing lower Rio Grande levees and through floodplain regulated by the IBWC (Essex 2008; Sherman 2008). Catastrophic flooding along the lower Rio Grande in 2008 and 2010 drew additional attention to the possibility that the barrier would exacerbate the problem (NBC News 2008; CBS News 2010). Counties in the Rio Grande valley entered into memorandums of understanding with the U.S. Section of the International Boundary and Water Commission (USIBWC) acknowledging its role in determining whether barriers were treaty compliant (Sherman 2008).

As the barrier construction project moved forward, the issue came to head in 2011 when Comisión Internacional de Límites y Aguas Entre México y Estados Unidos (CILA), the IBWC’s Mexican section, challenged DHS’s revised designs for barriers adjacent to the Rio Grande in Hidalgo and Starr counties — arguing the proposed barrier “constitutes a serious obstruction and deflection of the Rio Grande flows towards Mexico” (Rascón 2011). The USIBWC nevertheless approved the plans, asserting that their diagnostics, which used state of the art flood modeling, indicated no boundary deflection under flood conditions (John L. Merino, letter to Billy Moore, Oct. 30, 2012; memorandum to Luis Antonio Rascón Mendoza, Feb. 3, 2012). Mexico noted the diagnostic software had not been approved by Mexico’s engineers, thus it lacked confidence in DHS and USIBWC assumptions (Rascón 2011). There the matter stood while DHS proceeded with fence construction. Mexico maintained its concerns but refrained from publicly raising the issue during the Obama administration as sustained drought eclipsed flood worries on the middle and lower Rio Grande (Roberto Salmon, email to Stephen Mumme, Nov. 29, 2023).

The issue sparked anew in 2019 as private actors joined in barrier construction at two locations along the river, at El Paso, Texas, and Roma, Texas. Controversial anti-immigration nonprofit, We Build the Wall (WBTW), contracted a North Dakota engineering firm, Fisher Industries, to build a bollard style wall on a 3-mile stretch of land acquired by WBTW along the Rio Grande near Mission, Texas (Powers 2022). Fisher submitted a vague hydraulic impact assessment to the USIBWC in November 2019 that the agency quickly challenged, requesting more precise data, and specifying the hydraulic model to be used (Gentsch 2019; Rebecca Rizzuti, email to Greg Gentsch and Kris Kobach, Nov. 15, 2019).

After initially signaling its intent to abide by IBWC standards, Fisher moved ahead with construction. This prompted the USIBWC to file a lawsuit with the Southern District of Texas claiming a treaty violation (Powers 2022).[3] Subsequent analysis by USIBWC indicated that the Fisher barrier would likely cause riparian deflection under flood conditions, though mitigating action could be taken to reduce the hazard. Fisher agreed to settle the issue out of court by taking mitigating actions and agreeing to comply with a USIBWC-prescribed inspection and maintenance plan (Klasfeld 2022; Powers 2022). Whether Mexico was satisfied with the solution is unknown. It is clear that the USIBWC study, later acquired by Pro-Publica, was far more critical of the Fisher fence design than the settlement suggested (Trevizo and Schwartz 2022). That assessment seemed to be vindicated in 2023 when riparian erosion threatened to topple a section of the structure into the river (Goodman 2023).

Operation Lonestar’s Riparian Impediments

From its launch in March 2021, Texas Gov. Greg Abbott’s Operation Lonestar promised to challenge federal authority for immigration and border security enforcement along the Rio Grande. Abbott ramped up the pressure in May 2021 when he issued a disaster declaration authorizing the deployment of Texas’ National Guard to the boundary (Hernandez 2022; Gonzalez and Coronado 2023). The declaration justified the state’s decision to take unilateral border enforcement measures based on the alleged federal failure to stop the influx of unauthorized migrants entering Texas in 2020–21. Abbott followed with a program of state and privately funded barrier construction at various locations along the river, including the placement of shipping containers and concertina wire with the intention of deterring unauthorized entry to Texas. He did this without consulting the USIBWC.

The Giant Buoys in the Rio Grande

The conflict between Operation Lonestar and IBWC treaty authority came to a head in June 2023 when Abbott unveiled a plan to place a chain of giant spherical buoys in the center of the Rio Grande at Eagle Pass, Texas (Chazan 2023) (Figure 1).[4] Originally conceived by DHS officials during the Trump administration, the idea had been shelved on account of the likely legal complications in both domestic and international law. But the Abbott administration seized on this concept as a high-profile measure that would draw attention to the sharp spike in unauthorized entries along the Texas border. Again, the USIBWC was not consulted (Sanchez 2023a).

In this instance, however, both the placement of buoys and their design drew immediate and unequivocal condemnation by Mexico and the IBWC (Sanchez 2023b; Bach 2023). Issues included:

• An IBWC inspection that determined part of the buoys placed in the center of the river intruded on Mexico’s sovereign domain.
• The spikes separating each buoy on the chain were physically hazardous to anyone attempting to cross the barrier, raising humanitarian concerns.
• Submerged skirts beneath the buoys — and the way they were anchored to the riverbed — could trap debris and impede river flows, particularly in flood conditions.

Mexico, departing from its longstanding diplomatic posture of expressing behind-the-scenes concern but engaging in public forbearance on matters of boundary related treaty interpretation, publicly denounced the buoys as violations of the 1944 and 1970 treaties and humanitarian law (Roberto Salmon, email to Stephen Mumme, Nov. 29, 2023; Bach 2023; Higham 2023). It raised the matter directly with the U.S. Secretary of State and dispatched a team to determine if the 1,000-foot string of buoys intruded on the Mexican side of the river. It did.

The U.S. Department of Justice (DOJ) then sued Texas. While noting the potential treaty abuses, DOJ pinned its case on alleged violations of the Rivers and Harbors Act of 1899, a statute that placed permitting of works in navigable rivers under the jurisdiction of the U.S. Army Corps of Engineers (Knutson, 2023; USEPA 2023). Texas countered that the Rio Grande, at least in its Eagle Pass-Piedras Negras reach, was not a navigable river:

• On Sept. 6, 2023, a federal judge of the U.S. Western District in Austin, Texas, ordered the buoys’ removal, siding with DOJ (Miroff 2023; Rose 2023).
• Texas immediately appealed to the 5th Circuit Court of Appeals, which promptly granted a stay of action. However, a three-judge panel ruled against that appeal on Dec. 1, 2023, noting that the Western District court properly considered “the threat to navigation and federal government operations on the Rio Grande as well as the potential threat to human life the floating barrier created” (Beitsch 2023; Wiessner, 2023; Zhang 2023).
• Texas appealed the decision to the 5th Circuit’s plenary body and asserted that failing its appeal it would take the matter to the U.S. Supreme Court (Gonzalez 2023; Wallace 2023). The 5th Circuit, on January 17, agreed to grant Texas an En Banc (plenary) hearing (Wallace 2024; Weissner 2024).  The case will be heard in May 2024.

Figure 1 — Buoys on the Rio Grande

 

Figure 2 — Buoys on the Rio Grande and Concertina Wire on the Bank

 

Concertina Wire Along the Banks

Operation Lonestar’s use of concertina wire along the banks of the Rio Grande has also been challenged as a likely treaty violation (Villagran 2023; Flores and Weisfeldt 2023).[5] The deployment of razor wire barriers by Texas guardsmen and Texas Department of Public Safety officers began in 2022 (Gonzalez and Coronado 2023). Wire was placed atop existing barriers constructed by Operation Lonestar and, where barriers were distant from the river or otherwise nonexistent, adjacent to the river’s banks (Figure 2). The USIBWC expressed concerns about potential riparian deflection, as well as unauthorized encroachment on lands under its jurisdiction — most recently as guardsmen deployed additional wire along the river near the Texas-New Mexico boundary (Flores and Weisfeldt 2023).

The wire installations have also impeded Border Patrol agents from reaching migrants arriving on the Rio Grande’s north bank, forcing agents to sever wire in multiple locations to perform their duties. Again, the Abbott administration challenged these actions in court:

• In October 2023, it won a ruling ordering DHS to suspend wire-cutting pending further judicial review (Goodman 2023). 
• A subsequent ruling against Abbott’s appeal was itself appealed to the 5th Circuit, which on Dec. 4, 2023, issued a temporary stay of action pending further review (McDaniel 2023; Sanchez 2023b).  On January 2, 2024, prompted by several migrant deaths in the Rio Grande, the Justice Department appealed that decision to the Supreme Court. On Jan. 22, 2024 the Supreme Court sided with the federal government and allowed DHS to cut the wire as necessary to complete its mission (Howe 2024). 

Where Are We Now? Implications for US-Mexico Relations

At no time in its 175-year history has the boundary treaty system been so tested by problems originating outside the scope of the treaties, nor has it been so directly challenged by the unilateral actions of a subnational state which is not a party to the treaties. Arizona placed shipping containers along the boundary in 2022, but they were on land beyond the IBWC’s jurisdiction, and those barriers have since been removed (Alvarez 2022; del Bosque 2023).

Merits of Texas’ Case

While Texas’ measures are still being contested in legal proceedings, we are able to make several observations on the merits of the state’s case.

The Heart of Texas’ Claim. At the core, Texas’ claim to legal authority is an assumption that its public safety obligations — as codified in state law — should prevail when, as Texas alleges, federal authorities charged with immigration enforcement fail to act, placing an undue burden on the state. That assumption, anchored in a challenge to U.S. domestic immigration law, has so far been rebuffed by the U.S. Supreme Court, leading experts to expect a similar result if it is directly tested again (Gualandri 2022; Salam 2023).[6] But that is not the case currently pending in court.

Violation of the Rivers and Harbors Act of 1899? The case brought by DOJ, as mentioned above, is predicated on a claimed violation of the Rivers and Harbors Act of 1899 that requires federal permission authorizing barrier installation on or along navigable rivers. Texas has claimed its exemption on these three grounds:

1. The Rio Grande near Eagle Pass, Texas, is not a “navigable river” as defined in the act.
2. The floating buoys are not “structures” regulated by the act.
3. Texas is now invaded by migrants, thus justifying an exemption from national immigration law.

Judge David Ezra’s ruling of Sept. 6, 2023, granted the plaintiffs an injunction requiring the buoys’ removal and forcefully rejected all three arguments, noting that the determination of “invasion” is incontrovertibly a function of the national government, not the states.[7]

Structures on Rio Grande Banks and Floodplain. Questions about the placement of structures on the banks of the Rio Grande, or within a known floodplain, clearly fall within the scope of the 1970 Boundary Treaty’s Article IV requirement of IBWC review and joint approval. This applies whether the potential obstruction is metal or concrete walls or concertina wire.

National Perspectives

It is certainly preferable from Mexico’s perspective to see the Rio Grande River buoys issue resolved domestically, as Mexico’s Secretary of Foreign Relations, Alicia Bárcena, suggested after meeting with U.S. officials in August 2023. However, if DOJ were not to prevail before the court, it is likely that Texas would confront both the U.S. government and Mexico as virtually unified parties in defending application of the 1944 and 1970 treaties, regardless of national politics or parties in power.

This is because both countries have a strong incentive to restrict subnational autonomy in foreign affairs, particularly in the domain of territorial sovereignty. Neither country can abide unilateral and unauthorized assertions of state sovereignty interfering in contractual agreements between and among sovereign states. Such assertions and actions would undermine the reliability of national commitments and violate widely accepted norms of international law.

Likewise, both countries have a deeply vested interest in boundary integrity and maintenance. The 1944 and 1970 treaties express that interest, giving the IBWC both jurisdiction and administrative authority to interpret and apply these agreements. The 1970 agreement sets clear guidelines for the placement of barriers in the vicinity of boundary rivers. Neither immigration pressures nor border security concerns alter that fact. Property ownership in each country, even citizenship, turns on the clarity of location imparted by our shared boundary agreements. The ability to assign administrative responsibility for managing transborder flows, of goods and people, depends in part on the clarity of territorial demarcation.

Domestic and International Law Requirements

Domestically, U.S. courts are constitutionally required to give effect to treaties in which the U.S. is party (Bochard 1940). In this sense, treaty law enjoys standing as federal law and is covered by national supremacy provisions in Article 6 of the U.S. Constitution. Article 24 of the 1944 treaty expressly empowers the IBWC to invoke jurisdiction of the courts of either country, as necessary, to carry out its treaty mandate (Water Utilization 1944).

At the international level, the Vienna Convention on the Law of Treaties plainly establishes that treaties are binding agreements among contracting states (Kergis 1997). Article 27 of the convention affirms that a nation’s “internal law” is no justification for failure to abide by a treaty’s terms. Article 29 establishes that “a treaty is binding upon each party in respect of its entire territory” (Vienna Convention 1969). While the U.S. is not a party to the Vienna Convention, Mexico is, assuring that its principles would certainly be asserted in any bilateral dispute over treaty application (Banderas and Ochoa 2015).

In short, both national and international law favors the enforcement of treaty obligations over the concerns of subnational governments and their agencies.

Conclusion

The system of boundary and water treaties shared by Mexico and the U.S. is one of the crown jewels of their bilateral relationship. The 1970 Boundary Treaty, in particular, has allowed the two countries to place high confidence in their territorial sovereignty and the joint management of their riparian boundaries. The IBWC, with its authority to interpret and apply the 1970 Boundary Treaty, has clear jurisdiction to determine whether built structures or other obstructions in the vicinity of the treaty rivers affect the location of the boundary or not, and to decide — subject to the U.S and Mexican governments’ assent — whether rectification is necessary. Subnational governments may be consulted but, as they are not parties to the treaty, have no standing in these determinations.

The 1970 Treaty assures the integrity of sovereign territorial limits, and in doing so strengthens the ability of both countries to effectively apply other policies — including those related to immigration and national security. Recent challenges to the authority of the IBWC are short sighted in terms of their potential to fan dispute over treaty implementation with adverse ramifications for bilateral relations. They would also expose the United States to legal jeopardy were Mexico to challenge the placement of barriers in the Rio Grande by seeking a remedy in international law. Both countries are best served by honoring the boundary treaty system that has worked so well to secure their respective national interests.

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Notes

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[1] The agency has sections in each country. Comisión Internacional de Límites y Aguas Entre México y Estados Unidos (CILA) is under the administrative supervision of the Mexican Ministry of Foreign Affairs and is headquartered in Ciudad Juárez, Chihuahua, while the U.S. Section of the International Boundary and Water Commission (USIBWC) is a federal government agency based in El Paso, Texas.

[2] Each coastal state may claim a territorial sea that extends seaward up to 12 nautical miles from its baselines: https://www.noaa.gov/maritime-zones-and-boundaries. m

[3] United States v. We Build the Wall, Inc., No. 7:19-CV-403, 2019 WL 13191645 (S.D. Tex. Dec. 5, 2019), https://www.borderreport.com/wp-content/uploads/sites/28/2019/12/FedSuit.pdf.

[4] Each buoy is four feet wide.

[5] The Texas Department of Public Safety’s clearing of U.S.-held Rio Grande islands of invasive carrizo cane, trees, and other vegetation to assist with border security has also been challenged as proceeding without a permit.

[6] Arizona v. United States, 567 U.S. 387, 132 S. Ct. 2492, 183 L. Ed. 2d 351 (2012), https://www.oyez.org/cases/2011/11-182.

[7] United States v. Abbott, No. 1:23-CV-853-DAE, 2023 WL 5740596 (W.D. Tex. Sept. 6, 2023), aff'd, 87 F.4th 616 (5th Cir. 2023), reh'g en banc granted, opinion vacated, No. 23-50632, 2024 WL 174374 (5th Cir. Jan. 17, 2024), https://caselaw.findlaw.com/court/us-dis-crt-w-d-tex-aus-div/115027860.html.

 

 

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