A heavy fog permeated the coast as Paloma Aguirre rode the waves at Imperial Beach, rotating her bodyboard into them and flying off the lips.

"It's one of the best waves in San Diego County," Aguirre said of Imperial Beach, after her morning surf session. "If you want a powerful wave that has good shape and is consistent, this is where it's at."

The 40-year-old dual citizen of the U.S. and Mexico was runner-up bodyboarding champion at the national Mexican surfing games five years ago. She's been surfing since she was a teenager in Puerto Vallarta, Mexico.

"If I could, I'd spend all day in the water," Aguirre said.

She recalled the first time she saw brown water around her at Imperial Beach. It didn't concern her. She had been in brown water before, in Puerto Vallarta, where storms pulled earth off the mountainsides and darkened the ocean — just mud.

"When I moved here, I had the same assumption, and I didn't realize that sometimes when I went out in brown water, that was sewage water," she said.

RELATED: Cross-Border Sewage Spill Response Uncovers Ongoing Problems

For Aguirre, that is the downside of surfing in Imperial Beach: south-to-north flowing currents sometimes bring contaminated waters from northern Baja California, where water treatment infrastructure is aging and sewer pipes often collapse. Sewage spills and insufficiently-treated water discharged into the ocean can carry pathogens causing ear infections, gastrointestinal problems and more.

“It's really interesting because we have a line, a man-made line that we decided to put in place to separate both countries ... to the environment, to mother nature, it’s a joke … nothing’s going to stop the water," Aguirre said.

That line is three miles south of here, but the morning fog obscures the visibility of any distant line. The horizon seems to meld into the sky. The Imperial Beach pier appears to vanish midair.

One of Aguirre's favorite spots to surf is just a few yards north of the U.S.-Mexico border fence, where the steel has disturbed the coastal floor in a way that gives the waves there extra power. She said she often looks south and sees her Mexican friends surfing in Playas de Tijuana.

While the national debate around U.S.-Mexico border security has focused on the need to stop illegal immigration and drug trafficking, Aguirre has been trying to get elected officials to pay attention to a less-known cross-border flow: pollution.

Aguirre has become a leading local figure in the fight. She is the coastal and marine director for Wildcoast, an Imperial Beach-based nonprofit that organizes cleanups and awareness campaigns to improve water quality and other environmental issues.

She said the decades-long struggle to tackle the problem has been repeatedly hindered by a lack of binational collaboration.

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“You have two countries trying to address the issue in their own way and within their own judicial and legislative systems," she said. "You can have soft treaties or agreements ... but there's no real binding power behind it, in the sense that if they decide not to do it you can't take them to court.”

There’s been some headway. In the 90s, the U.S. and Mexico built an international sewage treatment plant in south San Diego County. It was upgraded in 2010. But the cross-border pollution problem has persisted, and it extends beyond the ocean.

Trash also piles up on land. When the Tijuana River floods, it brings everything from car tires to soda bottles onto an estuary in Imperial Beach. Aguirre visited the valley recently, and discovered a large yellow zucchini growing from the trash. She harvested it.

“Along with the sewage you get human waste, obviously, and seeds that come out of that and germinate throughout the valley, and the conditions are pretty good for produce," she said, tossing the vegetable in her hands. "So, yeah, zucchini."

Aguirre said she hasn’t lost hope that a solution can be found to protect the environment on both sides of the border – something more lasting than the never-ending cleanups.

Wildcoast is advocating to save the Border Wastewater Infrastructure Program, which would help renovate Tijuana's old sewer pipes and other Baja California water infrastructure. The Trump administration plans to cut funding for the program next year.

“It’s a beautiful resource, I think it’s both countries’ responsibilities to protect," she said. "The environment knows no borders.”

For Paloma Aguirre, water quality problems and other environmental issues tied to Mexico are personal and affect her day-to-day life in Imperial Beach.

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