Tijuana Sewage Crisis: Upstream Failures Undermine Downstream Fixes, Experts Say

For more than three decades, U.S. officials have focused on expanding the South Bay International Wastewater Treatment Plant in San Ysidro to stop sewage-laden flows from Tijuana that contaminate San Diego County beaches and sicken thousands.

However, experts argue this approach is fundamentally flawed because the real problem lies upstream in Tijuana, Mexico.

"I don't think there's any realistic scenario where downstream investments alone can solve this problem," said Paul Ganster, professor emeritus at San Diego State University's Institute for Regional Studies of the Californias, who has worked on transborder sewage issues since 1980.

Congress recently appropriated over $600 million to repair and expand the South Bay plant, and the Environmental Protection Agency signed an agreement last year to "permanently end the Tijuana River sewage crisis." But the funding and agreement won't prevent pollution from the rapidly growing Tijuana metropolis, which exceeds the capacity of the South Bay plant and a smaller plant on the Mexican side.

The crisis requires funding for infrastructure, operations, and maintenance to capture residential and industrial wastewater upstream in Tijuana, Ganster said. "This funding has never materialized," he added.

A report from the San Diego Regional Chamber of Commerce reframes the debate around the source of the problem: an aging, underfunded wastewater system in Tijuana with failing pipelines, overtaxed pump stations, limited treatment capacity, weak asset management, and no reliable long-term funding. The conclusion is unavoidable: as long as the upstream system remains broken, no amount of downstream investment can solve the crisis.

The Tijuana River watershed spans about 1,750 square miles, roughly three-quarters in Mexico. Tijuana, home to more than 2 million people, sits on hills and mesas draining north across the border into the Tijuana River Valley in San Diego and out to the Pacific.

Once sewage escapes the leaky, overburdened system in Tijuana, gravity sends it into the United States.

The South Bay plant, completed in 1997 when Tijuana was about half its current size, was designed as a safety net, not a primary solution. When the current expansion is complete, it will be the largest plant handling Tijuana wastewater—and still not big enough.

When border collectors are overwhelmed by spills, flows from unsewered neighborhoods, or heavy storms, raw sewage bypasses the plant and enters the Tijuana River and ocean.

The chamber's report says more than three-quarters of Tijuana's sewer network requires urgent rehabilitation, and 55 of 72 major pipelines need immediate attention. More than half of the city's pump stations require short-term repair.

Parts of the city have no sewage system at all, with raw sewage flowing directly into the watershed.

Tijuana's population is projected to rise from about 1.8 million in 2020 to 2.4 million by 2050, with wastewater flows expected to increase from about 67 million gallons a day to about 92 million—far beyond current treatment capacity. A smaller treatment plant in Tijuana, capable of managing 18 million gallons per day, was inoperable until recently due to severe disrepair.

More than $1 billion has been spent or allocated to the downstream solution centered on the South Bay plant. Since 2020, Congress provided another $300 million, bringing the expansion package to roughly $650 million.

However, the report warns that chronic underfunding of operations and maintenance will perpetuate failures even after major capital investments.

Tijuana's sewage system is run by the state of Baja California through CESPT, the state-owned utility, which is under severe financial strain. About 96% of its revenue comes from service fees, yet those revenues fall short of maintaining the system.

Federal funding from Mexico is limited and difficult to access.

Kenia Zamarripa, vice president of international and public affairs for the chamber, said, "When you look at the problem upstream, we are not yet aligned with the level of investment that's actually required. We're still largely reacting when the crisis becomes impossible to ignore."

In a 2022 binational agreement, Mexico pledged roughly $144 million toward sanitation projects, but only about $51 million has been secured. On the U.S.

side, only $4 million was spent on maintenance at the South Bay plant between 2010 and 2021, even as assets deteriorated. A 2022 assessment found 36% of the plant's assets in critical condition.

Ganster and others believe only a local binational border wastewater agency with dedicated, long-term funding can build, operate, and maintain a collection and treatment system for sewage flows that cross the international boundary. The International Boundary and Water Commission, which operates the South Bay plant, is constrained by its place within the U.S.

State Department and political crosscurrents in Washington.

Jeff Crooks, research director for the Tijuana River National Estuarine Research Reserve, said the persistent failures in Tijuana's sewage infrastructure demand an approach not focused on U.S. side investments.

"I can't imagine this would be a viable long-term solution," he said.