A spill that originated in the Tijuana River in Mexico flowed north of the border, releasing 143 million gallons of sewage for 17 days. The spill was caused when a sewage pipe under rehabilitation ruptured at the juncture of Mexico's Tijuana and Alamar rivers. While three-quarters of the Tijuana River watershed is located in Mexico, it drains into the Pacific Ocean near Imperial Beach, California.

"It's horrible. Everybody is complaining about it. People are really upset with the smell," Imperial Beach resident Lidya Morales told FOX 5.

"This is the worst spill we've had in over a decade," Imperial Beach Mayor Serge Dedina exclaimed.

After receiving complaints about the odor, Dedina sent a written inquiry to the U.S. Section of the International Boundary and Water Commission (IBWC). The agency then provided him a report regarding the spill.

"It's a major communication failure. It's obviously something they knew for a very long time," Dedina said. "Border authorities charged with managing sewage infrastructure and reporting these spills must do better and be held accountable for this act," the mayor said as he called for the resignation of IBWC chief Edward Drusina for his poor management of cross-border wastewater issues.

"It's outrageous that we have sewage spills of this magnitude occurring under the watch of the IBWC, and it's equally outrageous there aren't proper procedures in place to notify the public when sewage releases occur," Matt O'Malley of the San Diego Coastkeeper told EcoWatch.

"This is not just an environmental failure—it's a failure to protect the public health of those who live, work and recreate along the Tijuana River, Imperial Beach and beyond. The circumstances surrounding this spill and the failure to timely release information related to it should be investigated and prevented from happening again. Officials on both sides of the border must make sewage infrastructure in the region a top priority."

Coincidentally, local South Bay beaches were already closed due to sewage run-off from the recent rainstorms. A 2012 sewage spill caused by a similar Tijuana pipe breakage, which spewed almost 3 million gallons of sewage into the Pacific, had closed Imperial Beach for several days.

A portion of the Tijuana River near the San Diego-Mexico border, full of trash and debris. Susan Murphy, KPBS

This highly polluted river has many sources and is a persistent issue, which has cost the U.S. and Mexico hundreds of millions of dollars. Since the 1990s, the U.S. and Mexico have created programs to cooperatively address the issue, including the Minute 320 accord, which established a "general framework for binational cooperation" between the countries "on transboundary issues in the Tijuana River Basin."

Some areas in Mexico, including Tijuana, currently lack sufficient sewage infrastructure and garbage collection, and some residences do not have any form of plumbing. Along with population growth, this "has resulted in large amounts of human and industrial sewage, plastics and other forms of garbage accumulating in the river," Western Washington University's Huxley College of the Environment explained. Factories in the Mexican state of Baja California also contribute to pollution in the Tijuana River, KCET reported.

The river is bisected by the current U.S.-Mexico border wall, which President Trump plans to expand. The 2008 reinforcement of this wall "razed entire mountaintops and used the earth to fill in gulches and canyons," increasing erosion and contamination issues, KCET said.

"Significant improvements in the arena of wastewater treatment in recent years have improved water quality on both sides of the border," the Surfrider Foundation said. Unfortunately, storm water still brings substantial amounts of pollution into the Tijuana River Watershed. Their "No Border Sewage Campaign," which started in 2008, seeks to address this issue through outreach, networking and education.