Rio de Janeiro’s main Olympic neighborhood stinks. Literally.

For the last few weeks, residents of Barra da Tijuca, home to the main Olympic park and Olympic village, have woken to the fetid smell of filthy water.

Local biologist Mario Moscatelli blames the latest stink-fest on a couple of huge swells that battered Rio last month. They sent waves into the city’s inland lagoons, where they churned up the seabed and released noxious gases and filth — including layers of human waste — from underwater.

“Excuse my frankness, but the rivers feeding into the lagoons are pure sh--,” Moscatelli wrote in an email, “the feces of thousands of people emptied into the river without treatment.”

The swells, along with peak high tides, also helped rupture an “eco-barrier” — a temporary floating device that traps garbage flowing from inland into one of Barra da Tijuca’s main lagoons. The result: Piles of trash flowed out of the mouth of the lagoon onto one of Rio’s most iconic and most visited beaches a couple of months before the Summer Olympics.

This charming scene happened to coincide with the arrival of the Oi Rio Pro, a top-tier surfing competition and the pride of Brazil’s thriving surf culture. In the days leading to the tournament, dozens of municipal workers scrambled to clean the beach before the world’s top surfers, and thousands of fans, showed up.

But they couldn’t do anything about the slick of brown, smelly water flowing toward the contest site. The organizers moved the first days of the event to Grumari, an idyllic beach about 45 minutes away.

It’s just the latest foul water story to trickle out of this megacity. Last year, scientists said waterways including Guanabara Bay — an Olympic venue — were so filthy they were not safe for human contact. Even the fish hardly want to swim there.

Moscatelli blames the city and state governments of Rio for their abject failure to provide decent sewage treatment facilities and trash collection in local waterways. The city responded to our questions by blaming the state government. The state didn’t respond to calls for comment.

But we did reach Adrian “Ace” Buchan. He’s one of the world’s top surfers and is currently 10th on the official World Surf League rankings. Buchan is the league’s appointed “surfer’s representative.” An edited, condensed version of the interview follows.

Will Carless: You’ve surfed in Rio before. Have you ever gotten sick from it?

Ace Buchan: Yes, I got sick last year and the doctor at the event told me he believed it was from exposure to the water. I was really dizzy and nauseous the day I had to surf and nearly pulled out. A few months later in Tahiti, I was still having problems with my stomach and had to go on antibiotics.

I got sick again this year and the doctor was unsure whether it was food poisoning or the water.

(Here’s a video filmed May 4, just days before the surf contest, from the jetty at the far eastern end of Barra da Tijuca. It shows dirty water and trash flowing out of an inland lagoon into the ocean about 2,000 feet from the main competition site.)

Carless: Scientists have found shocking levels of contaminants in the city’s water and raised health concerns for Olympic athletes who will have to compete in the city’s water. Tell us what it was like for you and fellow surfers after coming in contact with it.

Buchan: There were roughly 12 surfers last year that fell ill and had very similar symptoms to me. Nausea, dizziness, vomiting, diarrhea.

That’s nearly a quarter of all the competitors, male and female. Yes it definitely led to concerns about the surfers competing there and I know it affected the decision of some of the guys not to come this year.

Carless: You’ve surfed worldwide. How does Rio’s water compare to other surfing competition venues around the world?

Buchan: It doesn’t compare. It’s undoubtedly the dirtiest water we surf in but it’s the only major city we compete in, too. Regardless, I think the water situation in Rio is dire.

(Here’s another video showing the extent of the trash and plant debris blanketing the beach. Bear in mind, this was taken mid-morning on May 4, after municipal workers had already been clearing the beach for hours. And, please excuse the shaky phone camera work.)

Carless: OK, now that we’re totally grossed out. Any advice for the athletes headed to Rio for the Olympics this August?

Buchan: I would say, be careful. The water isn’t going to get any cleaner between now and then. The situation has the chance to ruin an athlete’s Olympic dream. It happened to several of the surfers last year. Hopefully the Olympics can be the catalyst for change and bring some global awareness to the situation there in Rio, because it’s such a magnificent city with so much to offer. I love their beach culture and the melting pot of action on Rio’s beaches, so it would be a real travesty to lose that.

(Here’s another video showing black water flowing directly into the Lagoa da Tijuca. This once-crystalline lagoon, which flows far inland from the beach, is now flanked by Olympic infrastructure projects, including a new metro that will shuttle people to and from Barra and the tourist neighborhoods of Ipanema and Copacabana. If recent conditions are any guide, the view from the windows of those metro trains won’t be too lovely.)

Carless: Doubts are already circulating in the surfing media about whether Rio will host another surfing competition in the future. What would you say to the government and the people of Rio about this situation?

Buchan: It seems like a complex problem but there needs to be real action and investment from the top down if they want to fix it.

It’s a shame because Rio has some of the most beautiful beaches and scenery that I’ve seen anywhere in the world and the waves are good and the vibe on the beach and in the water in really special. However, the health concerns are threatening to kill the surf tourism and the local surf scene as well.

That would be a shame because the surfers and surf fans in Rio are some of the best in the world. They are really proud of their city and stoked to have us there but I had several educated local surfers apologize to me and my friends about the dirty water this year.