File photo. Caution signs at Coronado Beach warning residents of the polluted ocean. Photo by Madeline Yang.

Problems with raw sewage coming from Tijuana into the United States and onto San Diego County beaches, including Coronado, have gone on for decades. Here’s a truncated list of the numerous failures to fix the environmental crisis.

Early Years

March 1, 1889: The U.S. and Mexican governments agree to establish the International Boundary Commission, designed to maintain a peaceful, well-defined boundary between the two nations.

1934: The U.S. and Mexican governments instruct the International Boundary Commission to cooperate in the preparation of a report on the Tijuana sewage problem.

1935: Tijuana builds a new community septic tank designed to accommodate the wastes of 5,000 people. This project comes five years after Mexican federal census figures have revealed the Tijuana population to be 11,271. 

1938-39: Mexican and American officials decide it would be better to dump septic tank effluent from Tijuana directly into the ocean (rather than letting it first flow through the Tijuana River estuary). 

A Tijuana canal outlet of the wastewater going directly into the Pacific Ocean. Photo by Madeline Yang.

Feb. 3, 1944: The United States and Mexico sign a treaty for the utilization of water from the Colorado and Tijuana rivers and the Rio Grande. The governments agree to give “preferential attention to the solution of all border sanitation problems.” 

1948: Tijuana has almost 60,000 residents and no sewage treatment other than the septic tank built for 5,000. Americans complain about poorly treated flows coming through the outfall.


1952: A San Diego County report recommends connecting Tijuana and San Ysidro to the treatment/disposal system proposed for the San Diego metropolitan area.

Nov. 18, 1953: San Diego Regional Water Pollution Control Board conducts an investigation and finds water quality in the Pacific Ocean near the international border “has been seriously impaired for beneficial recreational use as a result of the discharge of essentially raw, undisinfected sewage from the International outfall sewer,” and 95% of the discharge generates from Tijuana.

December 1953: About 3.5 million gallons a day of poorly treated sewage is flowing through the international outfall. 

June 1954: A bond issue for construction of the San Diego Metropolitan Sewage System (including a Tijuana connection) fails because of controversy over the proposed location.

July 1954: The governor of California asks the U.S. State Department to file a formal protest with the Mexican government over the sewage issue.

1954: San Diego County’s public health department starts chlorinating the discharge at the outfall.

May 1955: The IBWC and its Mexican counterpart are authorized to investigate the problem. Investigation carries on for more than a year. 

Early 1958: Tijuana agrees to remove solid wastes and scum from its septic tank, while the San Diego County Health Department plans an intensified chlorination program. It functions from May 29 through September 14, when the county runs out of money. One week later, water quality along the beaches has reached unsatisfactory levels again.

Trash being treated at the South Bay International Wastewater Treatment Plant in San Ysidro. Photo by Madeline Yang.

March 1958: California governor again asks the State Department for emergency action. The State Department talks to Mexico, whose officials say they’re studying the problem.

April 1959: The California Legislature asks the U.S. government for help in correcting the pollution problem.

August 20, 1959: San Diego County Health Department finds that Mexico is not removing sludge and scum from the septic tank. The county closes all beaches from the border to the north end of Imperial Beach.

September 1959:  Mexico announces it doesn’t want to be connected to San Diego’s new sewer system. They say instead they will build oxidation ponds and reclamation facilities in Tijuana. They say this project will cost only half a million dollars and can be completed in nine months.

October 1959 — The Mexican federal government assumes responsibility for operating Tijuana’s septic tank, at the same time cleaning it and installing new sludge pumps. 


Dec. 1, 1961: Mexican officials begin running a new pump station, which transports sewage to the partially finished southbound canal.

January 1962: Mexico runs out of money to complete the open canal. Work on the canal stops at a point about 5.5 miles south of the border. Here the raw sewage flows down an arroyo, across the beach, and into the ocean.

Spring 1962: The Tijuana pump station fails, and all of the city’s raw sewage flows across the border. Talk of an “emergency connection” to the San Diego metropolitan system begins.

April 1965:  Storm run-off severs Tijuana’s force main, and raw sewage flows north again.

December 1965:  San Diego and the Mexican federal government reach an agreement to build an emergency bypass system, to divert Mexican sewage to Point Loma for treatment and disposal when the Mexican pump station fails. 

October 1966: Work on the emergency bypass is completed.

Oct. 10, 1966: Heavy rains cause a rupture in the Mexican force main that carries Tijuana sewage toward the coast. The emergency bypass to Point Loma is used.


1971: The emergency bypass is being used several times a day. 

March 1972: Mexico installs new pumps at their pumping stations and announces plans for improving the open canal. 

January 1973:  Mexico announces plans for an elaborate treatment plant to be located 15 miles southeast of Tijuana, at a cost of between $4 million to $8 million. Construction is scheduled to begin later that year, but lack of funding causes an indefinite postponement.

April 30, 1975:  The Mexican press reports that a new sewage treatment plant is under construction a few miles south of Tijuana. But once again, lack of funding causes this plan to be abandoned, and the septic tank built in 1935 remains the city’s only sewage treatment facility.

February 1978: Failure of a pipeline causes raw sewage to spill into Smuggler’s Gulch.

Executive Officer of the San Diego Regional Water Quality Board Dave Gibson in front of Smuggler’s Gulch. Photo by Madeline Yang.

May 1979: Tijuana’s main pumping station experiences a major failure, and the open canal washes out 3.2 miles south of the border. From this time on, 70%  of Tijuana’s sewage is routed to the emergency bypass and the remainder flows across the border in a number of places.


January 1980: Storms bring heavy run-off and water from Rodriguez Dam coursing through the Tijuana River, and the force of that tide breaks the 30-inch pipe that has been transporting the majority of Tijuana’s sewage to Point Loma. More than 15 million gallons a day of Mexican sewage stream through the Tijuana estuary and out to sea. The San Diego County Health Department quarantines four miles of beach, from the border up to the naval amphibious base.

1981-1983: Unusually rainy winters persist bringing many more sewage spills and quarantines. Dead farm animals washed up from Mexico are among the refuse found on beaches just south of Coronado.

April 14, 1982:  A “blue ribbon committee’’ is formed, consisting of representatives from a half-dozen American government agencies. They vow to abandon short-range thinking and come up with a permanent answer to the problem of Tijuana sewage spills.

November 1983:  A report is released from Lowry and Associates engineering firm. It concludes that the ultimate solution is for someone to build a treatment plant near the border that will process up to 130 million gallons a day of sewage — and cost some three-quarters of a billion dollars. Officials on both sides of the border are stunned by this figure. 

July 1984: The report on short-term and interim measures is completed. From among its offerings, the San Diego City Council endorses the idea of a 60-million-gallon-a-day, “bare bones” plant near the border that would cost an estimated $55 million.

Summer 1984: The California Legislature approves more than $5 million to go toward construction of the bare-bones plant. But the federal government grants only $5 million dollars with the promise of only $27 million more to come. 

Garbage collects on the side of a stream in a Tijuana canyon. Photo by Dennis Wagner.

Late 1984: As Mexico’s application for the $46.4 million International Development Bank loan approaches fruition, various American officials see this as a great opportunity to pressure the Mexicans into doing something about sewage treatment. 

April 1985: Lowry and Associates releases yet another study, this one of possible defensive measures, from which San Diego officials approve two ideas. The first $3.8 million project would rig a system to catch the renegade flows that come through the five border basins and canyons and then pump this sewage to Point Loma for treatment, until the second $31.6 million phase could be completed.

August 1985: The IBWC builds scaled-down “surface interceptors” for about $350,000, 

Jan. 28, 1987:  With enormous fanfare, Mexico “inaugurates” the first phase of the coastal treatment plant at Punta Bandera. 

Oct. 26, 1987: The Punta Bandera plant breaks down, as two of three large holding ponds develop leaks. 

March 8, 1988: The San Diego City Council gives “conceptual approval” to revised plans for the so-called Big Pipe. The concept for the pipe has now ballooned to a 12-foot-wide conduit that could carry more than 600 million gallons per day.

May 1988:  Treatment at Punta Bandera returns to full operations.


July 8, 1990: U.S.and Mexico International Boundary and Water Commission authorize construction of the South Bay International Wastewater Treatment Plant. The total cost was $256 million, with the U.S. paying nearly the entire bill.  

1994: Construction begins on the South Bay International Wastewater Treatment Plant in San Ysidro.  

April 16, 1997: U.S. and Mexico International Boundary and Water Commission agree to the distribution of construction, operation and maintenance costs for the international wastewater treatment plan.

January 1999: The South Bay International Wastewater Treatment Plan, which on average can handle 25 million gallons per day of sewage, completes a 4.5 mile long, 11-foot diameter pipe that discharges treated waste into the Pacific Ocean. 


Oct. 5, 2015: U.S. and Mexico International Boundary and Water Commission agree to a general framework for binational cooperation on transboundary issues in the Tijuana River Basin. 

Feb. 6-23, 2017: More than 143 million gallons of raw sewage was discharged into the Tijuana River upstream in Tijuana, polluting the Pacific Ocean and affecting southern San Diego County coastlines in Imperial Beach and Coronado. 

Caution signs at a beach in Coronado warning residents of the polluted ocean. Photo by Madeline Yang.

2018: Imperial Beach, Chula Vista, and the Port of San Diego filed the first lawsuit against the International Boundary and Water Commission, with subsequent suits filed by San Diego, Surfrider Foundation and others regarding sewage and chemicals polluting San Diego area communities and beaches. 

January 2020: Congress enacts the United States-Mexico-Canada Agreement Implementation Act, which appropriated $300 million for the construction of infrastructure to reduce the amount of polluted water flowing to U.S. sections of the Tijuana River Valley. The EPA is responsible for spending the money. 

April 12, 2022: Imperial Beach, other cities and government agencies announce a settlement has been reached with the U.S. Section of the International Boundary and Water Commission to mitigate raw sewage and chemicals polluting San Diego area communities and beaches. 

July 2022: U.S. and Mexico agree to “reduce transboundary wastewater in the Tijuana River watershed and Pacific Ocean through a suite of infrastructure projects on both sides of the border.” The agreement calls for expanding the South Bay International Treatment Plant so it can double the capacity of sewage treatment.  

December 2022: Congress authorizes $300 million transfer from EPA to IBWC to allow construction of expanding the wastewater treatment plant at the border.

Sources: Records from municipal, county and federal governments. Steve Schoenherr of the South Bay Historical Society. The Coronado News research. 

More News

The Coronado News is a 24-hour news website and direct-mail free newspaper to all residents and businesses of Coronado as we cover city government, schools, businesses, entertainment and the Navy.