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 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 crosses in dry weather.

But the pumps shut off when the river rises above about 23 million gallons a day, to protect them from sand and trash. In storms, flows average about 109 million gallons a day, and all of it crosses the border untreated¹.

2. The border canyons

West of the river, canyons like Los Laureles and Matadero run from Tijuana neighborhoods straight to the border. U.S.-run collectors there catch dry-weather flows and pipe them to the South Bay treatment plant³. When a pump station in Tijuana fails, or a storm hits, the collectors are overwhelmed and sewage and trash reach the estuary.

3. The coast at Punta Bandera

This is the route most people haven't heard of. The San Antonio de los Buenos plant, about five miles south of the border, receives roughly twice the sewage it can treat. The rest is discharged onto the shoreline, and ocean currents carry it north².

Why rain makes it worse

From November through April, storms push far more water down the river than anything 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 problem⁴.