How Tijuana's sewage reaches Imperial Beach

The short version

Most of the sewage behind beach closures comes from Tijuana, a city of more than two million people in its metro area, whose sewer system has not kept pace with its growth. It reaches Imperial Beach three ways.

1. 1The Tijuana RiverLeaks and spills flow down the river and across the border, mostly in storms.
2. 2The border canyonsSmall canyons carry spills straight to collectors at the border.
3. 3Punta BanderaUntreated sewage dumped on the shore 5 miles south drifts north.

1. The Tijuana River

In Tijuana, broken pipes, failing pump stations, and homes without sewer connections send sewage into the concrete river channel. Just before the border, a Mexican pump station called PB-CILA pulls that water out of the river¹. When it works, very little sewage crosses in dry weather.

But the pumps shut off when the river flow rises above about 23 million gallons a day, to protect them from sand and trash. In storms, an average of about 109 million gallons a day of sewage-contaminated water crosses the border without treatment, on EPA's 2015 to 2019 average². That is an average: individual storms can push the river past a billion gallons a day, roughly ten times higher, and the pumps stay off until flows drop back below about 23 MGD, which can take days or longer.

2. The border canyons

West of the river, canyons like Los Laureles and Matadero run from Tijuana neighborhoods straight to the border, where they become Goat Canyon and Smuggler's Gulch on the U.S. side. U.S.-run collectors there catch dry-weather water flows and pipe them to the South Bay treatment plant⁴. When a pump station in Tijuana fails, or a storm hits, the collectors are overwhelmed and both sewage and trash reach the estuary.

3. The coast at Punta Bandera

This is the route most people are less aware of, but drives much of the pollution found in the ocean on IB beaches. The San Antonio de los Buenos plant, about five miles south of the border, receives roughly twice the sewage it can treat. The half it can't treat is discharged, completely untreated, directly onto the shoreline, and ocean currents carry it north⁶⁷. The plant treats about 18 million gallons a day, roughly half of what arrives (2025–2026 reporting). You may see a larger number elsewhere: EPA's watershed page gives about 50 million gallons a day out of San Antonio de los Buenos Creek, which is total flow from before the 2025 rebuild.

Why rain makes it worse

From November through April, storms push far more water down the river than any of this infrastructure is built to handle, and the first storms wash out trash that clogs pumps and collectors. In dry months, the river is mostly under control when the pumps work, and Punta Bandera becomes the bigger problem⁵.