Mexico Said River Border Wall Broke Treaties. The US Built it Anyway.

Never again will crowds of migrants storm up the Tijuana River channel to cross into the United States like they did in 2018. 

Their way is now blocked.  

A piece of border wall President Donald Trump started in his first term is almost finished. Built as a bridge over the river for patrolling border agents, U.S. Customs and Border Protection, or CBP, designed this particular piece of wall like the entrance to a castle. One thousand feet of 30-foot-high steel gates cut across the notoriously polluted river’s concrete channel. Border agents are supposed to raise the gates before it rains.  

If they fail – say the power goes out, the gates won’t open and border agents can’t lift them manually – the force of billions of gallons of rainwater mixed with Tijuana sludge would smash against the wall-turned-dam, causing the raging river to back up over its levees and consume downtown Tijuana.  

That’s largely why this piece of wall has been incredibly controversial. CBP pushed forward with construction, even as Mexican officials alleged it violated multiple treaties and engineers warned the wall could cause catastrophic flooding of downtown Tijuana and San Ysidro on the U.S. side, according to records obtained by Voice of San Diego through a Freedom of Information Act lawsuit.  

Those records, which include hundreds of email exchanges, show the treaty violation allegations sent panic through the State Department. Government lawyers disagreed on whether the U.S. needed Mexico’s permission to build a wall through a river shared by two countries.  

At times, the International Boundary and Water Commission or IBWC – a key federal agency that owns and manages border lands on behalf of the U.S. — was caught off guard when CBP contractors began moving earth in the river channel the IBWC is charged with managing. And, throughout its construction, the U.S. Environmental Protection Agency relentlessly fought the wall which required very little study of impacts to the environment.  

Eventually, the IBWC and State Department rolled over on their concerns. The gated wall should be completed by March, John Mennell, a CBP spokesperson, told Voice of San Diego on Feb. 4. It’s been a dry 2025 so far. Whether the gates withstand future storms made worse by a changing climate has yet to be tested.  

Under Pressure: National Security Versus Flood Prevention 

A grossly underfunded federal agency, the IBWC was the only thing standing in CBP’s way of finishing the project. The Tijuana River and its levees are IBWC’s turf, so the burden of ensuring the river wouldn’t breach its channel with a new wall in the way was on IBWC’s engineers. 

There was enormous pressure to approve the project Trump’s first-term Homeland Security Secretary Kristen Nielsen said back in 2019 was necessary and in the interest of national security. 

Before the new wall, people crossing into the United States regularly walked up the river channel to surrender themselves to CBP officers on the other side. If you stand in the parking lot of Las Americas Premium Outlets in San Ysidro, where the border wall used to end, silver emergency thermal blankets worn by crossers litter the levee. Border agents complained in the past about getting sick after chasing people through the river water that’s tainted by untreated urban sewage from Tijuana. Then in November of 2018 during a surge of migration from Central America, hundreds of people tried to cross into the United States all at once through the channel as border agents fired tear gas upon them. 

“The opening in the border barrier in this location was a funnel point for illegal activity and a safety hazard for agents and illegal aliens due to the heavily polluted conditions of the river,” Mennell at CBP wrote in an email. 

Nielsen rushed wall construction projects like this one by waiving over 30 federal laws, including the Clean Water Act and the National Environmental Policy Act. President Joe Biden stalled the project and others like it in 2021, but allowed some – including the Tijuana River project — to resume again in 2022.  

Once the EPA learned the wall was back on the table, staff stepped in to prove erecting a barrier in a temperamental river was a bad idea. The agency hired a group of scientists to study the wall’s flooding effect left by the sweeping waiver. The final report showed building a wall would harm both countries, even under modest flood scenarios.  

In June of 2022, Dan Sainz, the IBWC’s liaison to Washington D.C., emailed his colleagues warnings from Doug Liden, an environmental engineer with the EPA who has worked on the Tijuana River issue for years. Liden flagged for the U.S. Consulate how CBP’s barriers caused major problems for both countries in the past.  

In 2019, CBP failed to hoist border gates at a drainage tunnel built through the border which caused massive flooding in Tijuana, triggering rescues and compromising key Mexican plumbing infrastructure that keeps sewage from contaminating U.S. beaches on the other side. And in 2014, sections of border wall designed to let water pass between Nogales, Arizona and Nogales, Sonora in Mexico killed two people and caused millions of dollars in damage.   

Congressman Juan Vargas — a Democrat who represents California’s 52nd District – asked Biden’s Secretary of Homeland Security, Alejandro Mayorkas, to stop the river wall in an Oct. 4, 2022 letter.  

“We have been told it is common for pieces of equipment to be stolen, causing the project to malfunction. We have also been told that CBP has frequently experienced gates jamming and malfunctioning,” Vargas wrote.” In this part of the river, any kind of malfunction would prove disastrous to the Border Patrol agents and other employees trying to find a resolution.”  

Nine days later in a letter to the IBWC, Adriana Reséndez Maldonado, in charge of Mexico’s version of IBWC called CILA, alleged the wall violated a 1977 agreement between the two countries as well as treaties from 1944 and 1889. She asked the IBWC to intervene and put a stop to its construction.  

“Mexico is against this proposed wall over the Tijuana River,” she wrote to her counterpart, Maria-Elena Giner, commissioner of the IBWC. “The negative effects … include floods, damages and loss of life in Mexican territory.” 

Mexico hasn’t changed its position since. In a December interview,  Alejandro Morales, the Mexican secretary of CILA, said the country has “always been opposed to the project. 

“A barrier that impedes a natural river channel, well, of course there’s going to be consequences,” Morales said.  

Reséndez Maldonado’s 2022 letter sent IBWC’s lawyers scrambling to figure out whether rubber stamping CBP’s border wall broke 133 years of promises with Mexico.  

At issue was whether Minute 258, an international agreement the countries signed in 1977, required Mexico’s approval for the U.S. Government to construct a security structure in the Tijuana River. The answer is yes, wrote Rebecca Rizzuti, the IBWC’s deputy chief counsel, to Elena-Giner. 

But in the 1848 Treaty of Guadalupe Hidalgo, which brought an end to the Mexican-American war, both countries also reserved the right to fortify and secure its borders at any point, Giner wrote to CBP, notifying the agency of Mexico’s disapproval.  

The IBWC apparently never resolved the issue. In responses to questions about treaty violations from Voice of San Diego, spokesman Frank Fisher wrote that IBWC engineers determined the river wall wouldn’t obstruct flooding waters through the river channel when the gates are open.  

Still, the 1977 agreement is pretty clear: Mexico and the United States decided the construction of fences or other works in the channel of the Tijuana River would have to be approved by both countries’ boundary and water commissions (IBWC and CILA) to ensure they don’t “obstruct the flow of water across the boundary.”  

“Mexico has a strong claim that it needs to be consulted on anything that would affect the movement of water,” said Stephen Mumme, a political science professor at Colorado State University and an expert on Tijuana River policy.  

This isn’t the first time Mexico’s alleged treaty-breaking related to United States border wall projects, Mumme said. But the country’s leadership hasn’t been willing to take the fight to the next level: Challenge the United States before an international court of justice.  

And there’s another broken treaty Mexico has yet to throw down, in Mumme’s view. In 1970, when the countries settled boundary disputes over the Rio Grande and Colorado River, it created consequences for promise breakers: If what either country builds in a river channel harms the other, the offending government has to remove it and pay for all the damage it caused.  

“Mexico is holding back, but that’s the next piece in the arsenal. That’s where they clearly have another card to play,” Mumme said.   

So far 2025’s been a pretty dry year for San Diego and northern Baja California. The river gate, and a complex set of agreements the IBWC forged with CBP to operate and maintain it, have yet to face a first test. 

“I know CBP is saying, we’ve got gates, we’ll take care of it. But that remains to be seen,” Mumme said. 

If the Gates Fail to Open 

CBP needed IBWC’s signature on a set of rules dividing responsibilities for how the wall would work before it could start building. The agency’s contractors planned to begin drilling in the riverbed on Dec. 7, 2022, read an email with the CBP staff names redacted. Any delay, they wrote, would cause extra costs for CBP. 

“You have my commitment to move as quickly as possible on my end,” Elena-Giner, the IBWC leader, wrote back.  

Chris McHone, with the State Department, assured his colleagues the agreements would “help put to rest the idea that this project is going to lead to widespread flooding.”  

“(It should) give everyone some confidence that they have a written commitment from DHS they can use to ensure the barrier is maintained and operated as designed,” McHone wrote. 

The IBWC prepared to greenlight the wall.  

In a Dec. 2 memo, Sally Spener, the IBWC’s foreign affairs secretary, told Jesus Luevano, the Mexican secretary, that it was up to his country to provide data or documentation showing the border wall would cause a flood in his country. CBP and IBWC had aligned on findings from a hydraulic study that apparently showed the wall wouldn’t increase the risk of flooding. The message to Mexico was: If you’re so worried about flooding, prove us wrong.  

Mexico didn’t get back to the United States with its data until February, but it didn’t matter. The project was already a-go. The IBWC inked its agreements with CBP on Jan. 26. 

From that point on it seemed everyone had trouble keeping track of CBP’s progress on the wall. At one point, the IBWC was caught off guard when bulldozers from CBP contractors began moving earth in the river channel. 

Construction began sometime around March 17, 2023, which also surprised the Department of State.  

“TJ River Barrier Now Under Construction (?!?)” read the subject line of an email from McHone, though the text of the email was redacted. Sainz, IBWC’s D.C. liaison, asked the IBWC if it knew anything about CBP’s construction plans. Morgan Rogers, IBWC’s operations manager in San Diego at the time, said contractors were trying to drill into the riverbed to fill the wall’s foundation but spring rains caused delays.  

Around that time, the EPA began to push back claiming all the flood modeling CBP had done was wrong. The agency didn’t consider 40-years-worth of sand and sediment that had piled up over time, which limited how much water the levees could hold before topping over even without a big wall in the middle.  

As private contractors, which included Kiewit and Michael Baker International, began to dig into the river bottom in April, the EPA released its studies showing the flood risks.  

By May, the State Department still wasn’t clear whether the project would flood downtown Tijuana during some of the most intense rain scenarios, like a 500-year storm which means there’s a 0.2 percent chance of a flood that large happening every year. The IBWC leaned on the EPA’s study which showed the wall could raise flood levels almost 1 to 4 feet in Tijuana. 

The CBP promised that some gates in the wall were designed to break away during a less-intense, 100-year storm – the worst case scenario Border Patrol looked at. Break away gates should prevent the barrier from acting like a dam walling up water and debris.  

Then the wall got its first test: Hurricane Hilary came barreling toward southern California and northern Mexico. IBWC engineer Padinare Unnikrishna sent an email at noon on Friday Aug. 18, 2023, presumably to Border Patrol or its contractors though the recipients were redacted, warning  Border Patrol it left construction material lying in the riverbed.  

Two hours and no response later, deputy chief counsel Rizzuti sent another email.  

“Just FYI – there is a hurricane approaching,” she wrote. “I think your contractor has piled sediment on the U.S. side and there is concern that those could obstruct the high flows expected in the river tonight.”  

At 3:45 p.m., Border Patrol’s let IBWC know their contractors were moving their equipment out of the river channel.  

The storm hit Mexico by Sunday morning. Luckily it didn’t bring doom to either side of the border. 

Six months later, the border wall faced a second test: the Jan. 22 storm which devastated and displaced thousands in southern San Diego.  

Staff from EPA sent photographs of the full, raging river that almost swallowed the bridge’s pylons to the IBWC. Days after the rain, IBWC engineer Apurba Borah forwarded those photos to Paul Enriquez and Timothy Quillman with Border Patrol. That the wall wouldn’t worsen flooding was still in doubt. 

“The flow is estimated to be around 25-year flood. Just wondering if the structure with fully open position will allow passage of a 100-year flood without obstructing,” Borah wrote.  

CBP redacted the names of the respondents who assured IBWC that water from this storm and a worse one would pass below the top of the wall’s upper bridge deck. The water did clear the upper deck – just barely.  

Though the wall now stands near-completion, the winter of 2025 has so far proved to be very dry. Whether it’ll be able to withstand worse storms than it’s already faced remains to be seen.  

Mexico never did give their blessing to the river border wall, the IBWC confirmed to Voice. But the agency doesn’t believe Minute 258 or the other treaties Mexico alleged the United States broke apply to the river barrier as designed. A lot of that depends on whether CBP opens these gates according to plan.  

Reporter Vicente Calderón of Tijuanapress.com contributed to this report.