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Lia Thomas takes top seed in women's 500Y freestyle prelim (0:28)

Lia Thomas of Penn won the top seed in the 500-yard women's freestyle prelim with a time of 4:33.82. (0:28)

11:23 AM ET

Lia Thomas qualified for the 500-yard freestyle final with a small group of protesters outside.

In her debut at the championships, Thomas finished in 4 minutes, 33.82 seconds to qualify for the final. It was the first time she has improved on her time in the event since the December meet where she swam a 4:06, which was the top NCAA time of the season.

Protesters from Save Women's Sports gathered outside the Georgia Tech McAuley Aquatic Center to protest Thomas' participation. The protesters held signs that read, "Support fair sports for women and girls", while one protester wore a shirt that read, "That man is a cheat." Thomas competed on the men's team for three seasons.

Jeanna Hoch traveled from Denver to support women and girls. There is no single-sex competition anymore.

Spectators stopped to take photos with the group, and some accepted pamphlets and stickers to show their support.

Thomas made national headlines after she posted the nation's top times in the 200 and 500 freestyle in December. She won three titles in the 500 freestyle and was the top scorer of the meet. She is going to compete in three events at the NCAA Championships.

If she wins a championship in Atlanta this week, she will be the first known trans person to win a national title.

In the final on Thursday night will be Brooke Forde, who finished second behind Thomas in their heat and qualified sixth with a time of 4:18.19. As part of the 800 freestyle relay win, Forde has a national title at this meet.

Forde is one of the few competitors who have shared their perspective on swimming against her. In January, Forde released a statement in which she said she had no problem swimming against Thomas.

Forde said that he was going to swim his race the way he wanted to.

Iszac Henig qualified 15th in the 50 free for the final on Thursday night. Henig will swim the 100 free in Atlanta.

Kate Douglas set a meet record in the 50 free with a time of 20.87.