Gevvie Stone won her women’s singles sculls heat by a small margin Saturday to qualify for Tuesday morning’s quarterfinals. And lest you think the 31-year-old Massachusetts native took some foolhardy risk delving into Rio’s notoriously fetid waters, know this: Stone is a doctor.

Stone, who edged out Denmark and Lithuania for first place in her heat, graduated from Tufts University School of Medicine in 2014 and has been training on the Charles River in Cambridge, Mass., ever since. She penned a piece for The Players’ Tribune last month defending her decision to compete in the polluted waters of the Lagoa Rodrigo de Freitas.

“When people freak out, I try to tell myself that people rowed on the Charles [River] in the 1970s when you weren’t supposed to go near it,” Stone told For The Win. “A lot of us row on places in the U.S. where I wouldn’t recommend jumping in, anyway. Like Lake Carnegie in Princeton where the national team trains. It had off the charts levels of E. coli there.”

The pollution sullying Rio’s waters has been well documented. Untreated sewage and viruses festering in the Guanabara Bay led the United Nations to recommend that competitors spend as little time in the water as possible in these Olympics. No area is more contaminated than the Lagoa Rodrigo de Freitas — site of this month’s rowing competition — where the Associated Press reported levels of bacteria and viruses so high that consuming three teaspoons of water from the area would lead to severe stomach and respiratory illnesses.

Stone is well versed about all the risks, but she says she has come too far to pass up what will likely be her last shot at an Olympic medal. After leading Princeton’s varsity eight crew to an undefeated national championship, Stone put her acceptance to Tufts School of Medicine on hold so that she could train for the 2008 Olympics. She failed to make the cut.

Undeterred, Stone spent the ensuing years balancing med school and crew training. She ended up qualifying for the 2012 London Games, where she finished seventh.

Stone is considered a medal contender by dint of her fourth-place finish at last year’s world championships.

“I don’t take any of the concerns lightly. At all,” Stone wrote. “I’m a doctor, and I try to be very rational about everything. But how can I be completely rational about a once-in-a-lifetime (or in my case, a twice-in-a-lifetime) opportunity like the Olympics?”

Stone continued by pointing out that while high-profile athletes like professional golfers enjoy large salaries and regular exposure, many lesser-known athletes recognize the Olympics as the pinnacle of their respective sports. Jason Day, Dustin Johnson, Jordan Spieth and Rory McIlroy — Nos. 1, 2, 3 and 4 in the golf world rankings, respectively — all cited concerns over the Zika virus in their decisions to skip the Rio Games.

“I simply think that those of us who are from sports where the Olympics are the pinnacle of competition look at the issues in Rio differently than professional golfers — for whom an Olympic gold medal would be prestigious, but for whom a Masters victory would be even more prestigious — when considering whether to compete.”

Stone takes comfort in knowing that people who competed in a regatta in Rio last year are all in good health. Still, she’s not leaving much to chance this week.

“You take precautions not to get water onto your face or in your mouth or eyes,” Stone said. “You have to put your water bottle inside a plastic bag, that’s a big one. You make sure nothing your mouth is touching has touched the water. And then you clean your hands thoroughly . . . before you eat. You don’t touch your face until you’ve sanitized your hands. I’m going with tons of bug spray and mouthwash and hand sanitizer.”

When it comes down to it, Stone just needs to avoid ending up like the Serbian men’s team Saturday morning.