She may not be visible from the shoreline but ultra-endurance swimmer Catherine Breed is days away from making history: becoming the first person to swim the entire length of California.

As of Thursday afternoon, she was somewhere along the La Jolla coast, tallying well over 800 miles since July.

“I feel great,” she told KPBS last week, while taking a break from swimming in Newport Beach. “We are looking forward to the finish. And I’m trying not to focus so much on being done, but rather enjoying the last few days.”

But as she completes the final legs of her 900-mile swim, Breed is about to face the environmental crisis at the San Diego-Mexico border South County residents deal with every day: sewage pollution in the waters off Imperial Beach and Coronado from Mexico.

For years now, beaches are repeatedly closed due to exceedingly high levels of pollution and exposure has made some people sick.

“It’s just heartbreaking that there’s a beach in California that the people that live in that area can’t go to and stay safe and stay healthy,” said Breed. “It’s kind of interesting to think that I get to spend four months in the ocean, and there’s people who live near the ocean and can’t even spend four minutes in the water because it’s so dirty.”

Even before getting in the water, Breed said she and her team, a crew of about half a dozen people who follow her in a boat, were thinking about areas in the open Pacific where she could encounter danger.

“The pollution issue at Imperial Beach is something I've known about since day one,” said Breed. “It is identified in my spreadsheet of planning as a red flag zone, meaning something that we need to be hyper-aware of.”

Before reaching the waters off the San Diego County coast, the 33-year-old marathon swimmer encountered many other environmental issues most people don’t get to see firsthand.

“California has a coastal current that typically runs north to south,” she said. “There's historical data about that on NOAA. And this year, because of the ‘super’ El Niño, that current switched direction. And so the current is quite literally going against us the entire way.”

The unprecedented weather, including navigating tropical storms and hurricanes in the Pacific, Breed added, has been the hardest part of the swim.

She has also witnessed the effects of two large marine heatwaves located near the coast of California.

“It's very noticeable how the ocean temperatures are affecting wildlife. The humpback whales, the last time we saw them was up in Pismo, and I know that they typically do come a little further south. I've seen manta rays and devil rays, which usually aren't around like Malibu, Santa Monica, typically.”

Along the way, Breed has also collected plastic she has found in the water, such as balloons.

Courtesy of Catherine Breed

Catherine Breed has been swimming along the California coast since July. Somewhere off the Los Angeles and Orange County coasts, she finds Mylar balloons.

“As I've entered LA County and even as we're swimming through Orange County, there are so many balloons in the water. In one day motoring out, we picked up about ten Mylar balloons, and that's just in my swim route in about an hour.”

As she nears the border, Breed said she has a plan.

“One thing we do is we track some of the beach closures, and our plan right now is to be about a mile offshore,” she said. “So that should put me pretty far out from the pollution. And in addition, I'll take prophylactic antibiotics.”

The strategy could protect her, said Aurora Czajkowski, a marine chemistry student at UC San Diego’s Scripps Institution of Oceanography researching the cross-border sewage crisis. She grew up in Imperial Beach, where she learned how to surf long before the beach closed.

“When we have pollution enter our ocean from a river mouth, it is like, contained in what we call a plume,” she said.

The plume from the Tijuana River disperses in the coastal waters and can get trapped in the surf zone, Czajkowski said.

She hopes Breed’s swim brings national attention to a decades-long issue in her hometown.

“I hope that her journey will kind of highlight that the South Bay San Diego communities do have a lot to give to our communities,” she said. “And it's not just a dirty beach community.”

One reason for the California swim, Breed said, is raising awareness of ocean conservation issues like access to clean water.

“What I hope comes out of my swim is that the people in the community look to the groups, look to create their own group that are invested in cleaning up those waters and that they go forth and do that,” she said.

Throughout the swim, Breed has come ashore and talked to Californians about protecting the ocean. On Monday afternoon, she plans to celebrate swimming the 900-mile coast with a ceremonial finish in partnership with the nonprofit WILDCOAST in Coronado.