CAMBRIDGE, Mass. — Penn swimmer Lia Thomas won the 500-yard freestyle race at the Ivy League championships Thursday night, accelerating past her competitors to establish a new record for Harvard University’s Blodgett Pool.

The natatorium boomed with cheering athletes and fans as Thomas swam neck and neck with her competitors for the first part of the race. Around the halfway mark, Thomas took a significant lead and finished in 4 minutes, 37.32 seconds, about three seconds off her personal best, and edging the pool record by three-tenths of a second.

In second place was Penn sophomore Catherine Buroker, who posted a time of 4:44.83, a seasonal best. Princeton sophomore Ellie Marquardt — the defending Ivy League champion in the event — placed third in 4:46.63, and Penn junior Anna Sofia Kalandadze came in fourth in 4:47.54.

Thomas, a 22-year-old transgender woman, entered the Ivy League championships as the top seed in three events — the 200-yard, 500-yard and 1,650-yard freestyle. She holds the fastest times in the country among NCAA women in the 200 and 500 freestyle.

Her success has placed her at the center of a heated national debate on transgender athletes’ — especially trans women’s — rights to play sports.

» READ MORE: Penn swimmer Lia Thomas’ success has prompted national debate about trans athletes. Here’s what to know.

Thomas’ detractors — including some of her teammates — say that her male-at-birth assignment gives her an unfair biological advantage. Her supporters say that because Thomas has followed all eligibility protocols, including being on hormone therapy for more than two and a half years, she has a right to compete.

Quick facts on Lia Thomas

For a more comprehensive dive, read this explainer. Here are a few key things to know:

  • Thomas' swimming: Thomas swam on the men’s team for three years. Last season was canceled by the pandemic. This is her first year on the women’s team.
  • Hormone therapy: She started hormone replacement therapy in May 2019.
  • Eligibility: Thomas has fulfilled all the NCAA’s eligibility requirements to compete.
  • The science: Experts say a trans woman’s testosterone levels will fall to that of the average cis-woman’s between the first and second year on hormone therapy. Their strength levels will significantly drop, but will never fully equal an average cis-woman’s, they said.
  • What critics (including teammates) say: Her male-at-birth assignment gives her an unfair biological advantage, like height, increased lung capacity, and strength.
  • What supporters say: She’s successful because she’s a hardworking athlete, not because she’s trans. She's earned her spot to compete, and isn't stealing a place from other women.
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Last month, 16 of Thomas’ teammates wrote to Penn and the Ivy League asking that Thomas be barred from competing in this week’s race. And this month, more than 300 former and current collegiate swimmers, including five of Thomas’ teammates and a former Olympic swimmer, sent a letter to the NCAA in support of Thomas.

Last week, the NCAA cleared the way for Thomas to compete in next month’s NCAA championship meet. She’s the only Penn woman to qualify thus far.

» READ MORE: NCAA clears path for Penn swimmer Lia Thomas to compete in championships

In the back of the natatorium Thursday, Schuyler Bailar, the first openly trans Division I male swimmer, looked on, briefly draping a pink, blue, and white transgender pride flag across the bleachers.

Penn taking three out of the top four spots in the final was no surprise following a strong showing in the preliminaries, in which Thomas, Kalandadze, and Buroker secured the top three spots.

And in a show of sportsmanship during the preliminary swim, Princeton’s Marquardt and Thomas shared a fist bump.

The championship meet — which marks the end of the season for most of the women — kicked off with two relay races Wednesday night.

On Wednesday, Thomas made her debut in the 800-yard freestyle relay, swimming the first 200 yards. She barely trailed Yales’ Iszac Henig for most of the race, but Thomas steadily kept her pace, narrowly passing Henig at the end to win by just 0.15 seconds.

The thin lead didn’t last long. Penn ended up finishing third overall in that race, with Harvard taking first and Yale second.

Thomas’ individual time for her 200-yard portion was 1:44.50, about two seconds slower than her personal best time. Henig swam a personal best of 1:44.65, surpassing his previous best by nearly three seconds.

Henig is a transgender man who has not yet begun hormone therapy so remains eligible to swim on the women’s team. He has had a tremendous showing in the championship thus far, placing first in the 50-yard freestyle Thursday in 21.93 seconds — also a new pool record.

Penn also placed fifth in the 200-yard medley relay Wednesday. The Quakers were in fourth place overall among team points by the end of Thursday’s events.