IMPERIAL BEACH, California — Raw sewage teeming with toxic chemicals dumped in Mexico's northern border city of Tijuana has been flowing for decades into the United States while local, state, and federal authorities in both countries have failed to prevent it. Now, those on the front lines of this crisis are saying enough is enough.

Unrestrained run-offs of ugly green and brown liquids have caused both figurative and literal headaches for U.S. Border Patrol agents assigned to the Tijuana River Valley, a stretch of land south of San Diego from where the Tijuana River flows north from downtown Tijuana into California and then west to the Pacific Ocean. Some of the sewage is intentionally dumped in Mexico with the full knowledge that it will end up as a gruesome export to the United States.

“It’s been, like, 20 years it’s been a problem, but not until recently the residents of Imperial Beach are telling the politicians they need to do something about this beachfront property ... We’ve been dealing with it for decades," said Ralph DeSio, regional spokesman for Border Patrol's parent agency, U.S. Custom and Border Protection.

The smell — even on a sunny day when pools of water have dried up — is unforgettable. The liquid and soil the sewage runs through are also comprised of unsafe levels of toxic chemicals.

CBP commissioned a six-month study, published earlier this year, of 42 samples from the river and two culverts during dry, wet, post-rain, and standing water conditions. The run-off contained 710 times more arsenic, five times more lead, seven times more uranium, and 1,135 times more hexavalent chromium than local tap water. In addition, high levels of dozens of other chemicals were identified by the study.

Justin Castrejon, a Border Patrol agent and regional spokesman, said the report validated the claims of agents who have complained of physical health ailments after patrolling the affected areas. “It’s scientifically proven. Tests were done,” he said.

After the study, the agency moved to improve the situation for agents while they waited for the more senior authorities to address the problem. CBP has installed personal and vehicle wash centers at Border Patrol stations so agents could “reduce exposure to contaminants and minimize cross contamination” by hosing down after their shift and before driving out to main roads. Vehicles had special cabin filters installed to improve internal air quality.

Agents were also given personal protective equipment, including gloves, respirators, masks, privacy tents, disposable clothing, and towels.

“Oftentimes, agents sitting here all day will experience sore throats, headaches. That’s very common," said Castrejon. "Exposure has led to rashes."

In one case in 2010, an agent with direct exposure picked up a flesh-eating bacteria and retired for medical reasons.

Waste from Tijuana is primarily entering the U.S. by the Tijuana River and two separate culverts that are meant for drain water to run off into a parkland in Imperial Beach, from where it then makes its way to the ocean.

While touring each of the three spots where the liquids are flowing in, Castrejon, an advanced EMT, and this Washington Examiner reporter both became nauseated and light-headed standing near the run-off.

“Your blood is absorbing this stuff, not oxygen. Your O2 saturation is probably down a little bit. It should be at 96 and above," he said.

The first site, dubbed the "channel," is a concrete-laden storm drain a couple hundred feet wide. The river enters the U.S. between some shopping outlets and San Ysidro Port of Entry, then curves west toward the coast as it makes its way through this storm drain and eventually flee-flowing through a nature preserve to the beach.

“There shouldn’t be any water here without any rain,” said Castrejon, adding it had not rained in at least two weeks. “When there are rains, this will flow … We can safely say this is more or less waste water — illegal dumping in Mexico that is now flowing into the U.S.”

A tire mountain culled from waste entering the United States from Mexico. (Anna Giaritelli/WEX)

The National Guard has been called in through the years to clear out overgrown vegetation and the garbage left behind. A pile of hundreds of tires sits to the side of the storm drain. Castrejon said it is not unusual for whole refrigerators or car bumpers to pour through the storm drain.

About a mile west is a set of culverts for natural water flow or rainwater. This one is referred to as Steward's Drain. Liquid is flowing out of a 10 by 30 foot grated drain into an area known as Goat Canyon. From here, mass flows of polluted water push their way out to the coast through the preserve. Castrejon said he drove by a few weeks ago and observed water sitting in a pond-like area four feet high around the culvert.

“The soil and the dirt has been contaminated for so long, as soon as the wind picks up or you go by and kick it, it's not good to breathe in that dust," he said.

Castrejon said during even light rain storms agents must pull up grates that normally cover the drains to prevent people from illegally crossing into the country so that the flows can pass through. If the grates are not moved out of the way, large items will block the water from getting through.

Last December, a sewage collector in Tijuana combusted, and as many as 7 million gallons of raw sewage poured into the river daily for a week. Castrejon said large flows are not rare and frequently occur.

The Imperial Beach community is getting more vocal about its concerns because it regularly shuts down beaches every time it rains.

The San Diego Port, Chula Vista, and Imperial Beach have signed onto a San Diego Surfrider Foundation lawsuit against the U.S. International Boundary and Water Commission on the basis that the federal agency has violated the Clean Water Act by ignoring the problem for decades. The city of San Diego and California Attorney General Xavier Becerra have also sued. That case is expected to be heard by a judge next April.

In the meantime, CBP is working on getting results from a second water sampling.

“Where it stand with us as far as Border Patrol-wide — it’s just an ongoing effort to protect our agents from this exposure. We’re doing the testing. We have the results. And we’re doing everything we can do protect the agents," said Castrejon.