What reaches the ocean — IB Water Pollution

Four places discharge into the ocean off Imperial Beach. Three of them carry untreated sewage: the mouth of the Tijuana River, the shoreline at Punta Bandera in Mexico, and the small canyons along the border. The fourth, the South Bay Ocean Outfall, carries treated wastewater.

The four places that discharge into the ocean, sized by dry-weather volume.Open this view of the map

The short version

Source	Dry season	Storm	What it carries
Border canyonsGoat Canyon and Smuggler’s Gulch into the estuary	~0.5 MGD†	~8 MGD†	Raw sewage, Trash, Sediment
South Bay Ocean OutfallAbout 3.5 miles offshore	~35 MGD	~38 MGD†	Treated wastewater from the South Bay plant and a City of San Diego reclamation plant
Punta Bandera shorelineMexico, about 5 miles south of the border	~18 MGD	~22 MGD†	Raw sewage, Partly treated sewage, Industrial chemicals
Tijuana River mouthEstuary, south end of Imperial Beach	~1 MGD†	~109 MGD (2015–2019 avg.)	Raw sewage, Industrial chemicals, Trash, Sediment

MGD means million gallons per day. These are approximate averages; real flows vary a lot from day to day and storm to storm. Values marked † are our own rough estimates rather than official figures.

In dry months: Punta Bandera

When it isn't raining, the Tijuana River is mostly diverted before it crosses the border, as long as the PB-CILA pump station in Mexico is working. The bigger source is the San Antonio de los Buenos treatment plant at Punta Bandera, about five miles south of the border. It receives roughly twice the sewage it can treat, and the rest is discharged onto the shoreline. The recently rebuilt plant treats about 18 MGD (2025–2026 reporting), roughly half of what arrives. Ocean currents carry that plume north.

Modeling by the Scripps Institution of Oceanography, summarized by the EPA, found that Punta Bandera is the main source of the pollution behind beach closures in dry months. At about 18 million gallons a day, that adds up to something on the order of 6 to 7 billion gallons of untreated sewage a year. That annual figure is our own estimate from the published daily numbers, not an official one.

You may see a larger number elsewhere. EPA's watershed page says about 50 MGD flows out of San Antonio de los Buenos Creek. That is an older figure for total flow, from before the plant was rebuilt in 2025. The 18 MGD above estimates only the untreated share today.

In storms: the river

When it rains, the river rises past what PB-CILA can handle, and the pumps shut off to protect themselves from sand and trash. EPA data show that in storms an average of about 109 million gallons a day of sewage-contaminated water crosses the border without treatment (2015–2019 average). That is an average: individual storms can push the river past a billion gallons a day, and the pumps stay off until flows drop back below about 23 MGD, which can take days or longer. It runs down the river, through the estuary, and into the ocean at the south end of Imperial Beach.

In the rainy season, the Scripps modeling attributes about two-thirds of closure-causing pollution to the river and about one-third to Punta Bandera. Since October 2018, more than 200 billion gallons of sewage-contaminated water have crossed the border in the Tijuana River, according to IBWC figures cited by the California State Assembly.

The border canyons

Collectors in Goat Canyon, Smuggler's Gulch, and three smaller canyons catch dry-weather flows and pipe them to the South Bay treatment plant. When a pump station in Tijuana fails, or a storm overwhelms them, sewage and trash flow through the valley to the estuary. How much reaches the ocean this way is poorly documented.

What's in it

It isn't only human waste. Researchers have found viruses, antibiotic-resistant bacteria, and hundreds of chemicals in the water, including pesticides, solvents, and flame retardants. Much of this comes from industrial discharges. Enforcement of the rules on industrial waste in Tijuana appears weak: a September 2026 San Diego Coastkeeper report found a steady stream of industrial chemicals, heavy metals and pesticides in the river. The river also carries tons of trash and sediment: the trash boom just north of the border has stopped about 2,000 tons of trash and debris over two storm seasons.

From the water into the air

What reaches the ocean doesn't stay there. Research led by Scripps Institution of Oceanography at UC San Diego has shown that bacteria and chemicals from sewage-polluted water can become airborne in sea spray and come back onto land. Along the river, churning sewage releases hydrogen sulfide gas. Health covers what that means for people nearby.

What would change this

Fixing dry-season closures depends mostly on Punta Bandera, where an offshore outfall and plant expansion are being studied but aren't funded. Fixing rainy-season closures depends on handling storm flows, which no current facility is built for. The project tracker shows where each project stands.

What actually reaches the ocean