A 29-year-old woman running in the Dallas White Rock Marathon collapsed on Sunday and died, officials said.
Erin Lahr, of Austin, collapsed at the 21-mile mark of the marathon, race director Marcus Grunewald told The Dallas Morning News.
The cause of death was not immediately determined, according to the Dallas County medical examiner.
Grunewald said the death is the first in the 39-year history of the event.
The 26.2-mile certified course, which starts and ends near downtown Dallas, is mostly flat with some rolling hills. Temperatures on Sunday climbed to the mid-70s.