(AP) — For more than two weeks, a stench of feces, ammonium and laundry detergent emerging from a sewage spill wafted through the air in the southwestern corner of the continental United States.

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Residents who contacted government offices got no answers.

Finally, a U.S. official released a report that sparked a furious reaction: sewer repair work in Tijuana, Mexico, caused an estimated 143 million gallons to spill into the United States and the Pacific Ocean for 18 days. A Mexican official challenged those findings on Friday after a week of public uproar.

The city of Imperial Beach was most affected by what Mayor Serge Dedina called “the tsunami of sewage spills.”

At a raucous public hearing Thursday night, angry residents shouted at government officials and demanded answers. They said they were kept in the dark too long and are fed up with continued problems with sewage from Mexico that fouls beaches and endangers their health.

Who knew what and when is unclear. So, too, is whether the right communication channels were used to alert the public.

The International Boundary and Water Commission, a bi-national office that addresses border disputes over water and other issues, on Thursday promised a report within 30 days. The IBWC said its review will determine how much sewage spilled for how long and identify errors in communication.

Steve Smullen, the IBWC area field operations manager in San Diego who came up with the preliminary spill estimate, said a U.S. Border Patrol official alerted him to the stench Feb. 6 and he quickly notified a Mexican counterpart. U.S. officials say they didn’t get answers until Feb. 23, a day before the public announcement.

Roberto Espinoza, representative of the IBWC’s Mexican section in Tijuana, said at the community forum in Imperial Beach that he immediately began asking questions but the Mexican agency responsible for fixing the problem left him in the dark.

“There was a failure in the flow of information between the agency and us,” Espinoza said in Spanish. “It is very regrettable and painful to us.”

The Commission for Tijuana Public Services, an agency of Mexico’s Baja California state that did the repairs, says the sewage spill lasted only from Feb. 1 to Feb. 4 and that cross-border flows after that were stormwater. Miguel Lemus, the agency’s director, said the U.S. official’s preliminary estimate was far too high and that foul waters likely got trapped in the United States, producing the stench.

Lemus said in an interview that he should have briefed the IBWC’s Mexican representative before the repairs. He said he hoped the U.S. and Mexico develop better communication protocols “to avoid misunderstandings and the dissemination of information that is not totally accurate, like what’s happening now.”

Under an 1848 treaty, the Tijuana River crosses the United States for a few miles through a valley before flowing into the ocean. During high tides when sewage is heavy, residents say foul-smelling water fills an estuary.

Cross-border sewage has long been a sore topic in Imperial Beach, a city of about 30,000 that draws surfers and families looking for relatively affordable homes near the beach. As mayor in 1980, Brian Bilbray, who went on to serve in Congress, used a bulldozer to prevent the Tijuana River from flowing on to city beaches. Spills of more than 10 million gallons a day were common.

A U.S. plant that was completed in the 1990s — combined with improvements to Tijuana’s system — alleviated the problem, but the latest spill is a reminder that infrastructure is woefully inadequate. Spills of 1 million gallons or more are still considered routine.

David Gibson, executive director of the California Regional Water Quality Control Board in San Diego, on Thursday asked the U.S. Environmental Protection Agency to investigate the latest spill, with a focus on the Tijuana commission’s actions. He also wrote the North American Development Bank to ask for more attention to the region’s infrastructure.

“I am deeply troubled by the lack of communication that has characterized this event,” he wrote the U.S. and Mexican heads of the IBWC.

Promises to find answers have gotten a wary reception in Imperial Beach, which was overwhelmed by people entering the country illegally from a nearby canyon in the 1990s, before the U.S. erected one of the most fortified stretches of fence with Mexico.

Stephanie Pate, who has lived in Imperial Beach for all of her 37 years, said government hand-wringing over the sewage is “all lip service.”

“The town is getting better, but the pollution is still bad,” she said.