(NewsNation) — Lia Thomas smashed records for the University of Pennsylvania women’s swim team and made history in March, becoming the first transgender athlete to win an NCAA title.

Thomas swam her first three seasons on the men’s team, not as Lia, but as Will Thomas.

After transitioning, the fifth year senior won Ivy League championships and set Penn records in the 200 meter freestyle, the 500 and 1650 meter freestyle.

Thomas’ participation in women’s competitions had league administrators, and her teammates, bitterly divided.

A total of 16 members of the UPenn women’s team wrote a letter to those in charge, saying while they support Lia’s gender identity, “the biology of sex is a separate issue from someone’s gender identity. Biologically, Lia holds an unfair advantage over competition in the women’s category.”

In an interview with Sports Illustrated, Thomas pushed back at critics and said “the very simple answer is that I am not a man. I’m a woman. So I belong on the women’s team.”

One of Lia’s teammates agreed to speak with NewsNation, anonymously.

“I agree that Lia identifies as a woman. I think that there is differences between the physiological makeup of a transgender woman versus a cisgender woman. And to allow Lia, 100%, the ability to be on the women’s team with no rules, it’s not fair.”

USA Swimming announced new rules for transgender women swimmers — that they demonstrate testosterone levels below five nanomoles per liter for three years before competition. They must also provide evidence that they do not have a competitive advantage from being born male.

However, the NCAA announced that it would not change its own rules mid-season.

Tennis legend, and long-time champion of LGBT rights, Martina Navratilova spoke out against the NCAA decision, in an interview with NewsNation.

“It’s like everybody wants to swim as a female because it’s an easier … field, I think, to compete in. Lia, I don’t agree that she should be allowed to swim, but again, she’s going by the rules. So the rules need to change. Rules need to change because this is not a fair fight,” Navratilova said.

As of today, 7,605 people, some 400 Olympians and Paralympians, have petitioned Congress and sport governing bodies to prioritize competitive fairness and safety for biological women, while urging sport to develop structures to welcome all trasnsgender atheltes to participation in sports. https://drive.google.com/file/d/1eec_1id68zpwm9hphog2u5avr2ptxl_s/view?usp=sharing

Thomas responded to the critic in an interview with ABC, saying she knew there would be scrutiny if she competed as a woman.

“There’s a lot of factors that go into a race and how well you do and the biggest change for me is that I’m happy … sophomore year, when I had my best times competing with the men, I was miserable. So having that be lifted is incredibly relieving and allows me to put my all into training and racing,” Thomas said.

When asked about her 16 teammates who wrote in support of her gender identity, but against her competing against women, Thomas said “you can’t go halfway and be, like, ‘I support trans women and trans people, but only to a certain point.’ Where if you support trans women as women, and they’ve met all the NCAA requirements, then I don’t know if you can really say something like that.”

Lia’s former UPenn teammate, who spoke with NewsNation anonymously, responded.

“Lia saying that we can not support trans women ‘halfway’ is a ridiculous thing to say when females are losing real life opportunities due to transgender participation. Wanting to create a space for females to thrive with the capabilities they have received from female puberty is not threatening to trans women.

“There has to be separate competition if females want a chance at fair competition. It’s crazy to me that after all of this, Lia could still think that her anatomy is within the normal female variation. If Lia swims against men, no one is saying that is how she has to identify.”