A former Vanderbilt University track star and her sister are dead after falling off a pontoon boat and drowning in a Texas lake on the Fourth of July.

Teegan Hill was celebrating her 31st birthday Sunday night outside Dallas. She was on Lewisville Lake with 11 other friends and family, including her 28-year-old sister Troinee Broom, when their rental boat began taking on water after being hit by a strong wave.

Just before 8 p.m. the vessel began to tilt, causing both siblings to fall overboard, witnesses said.

Neither woman was wearing a life vest.

“Everything happened so fast. We went from enjoying her birthday and getting ready to leave to go home, to the boat being submerged in water and it’s tipping over,” said Thelma Anderson, a classmate of Hill’s who was at the party Sunday night.

A dive team with the Lewisville Fire Department recovered their bodies later the same night after a search that lasted about five hours, reports said.

The search team finally found the victims about 12:30 a.m. and pulled their bodies from the water about 800 yards east of Pilot Knoll Park in Argyle, according to the Tarrant County medical examiner’s report.

The tragedy remains under investigation. There was growing speculation of whether the boat may have been overcrowded and had too much weight on board.

“Our heart and prayers go out to the family members that they lost those two people this weekend,” said Highland Village Fire Department Chief Michael Thompson, according to Fox 4. “Unfortunately, Lake Lewisville is known for being a fairly dangerous lake.”

Hill, a native of Lancaster, Texas, attended Vanderbilt from 2009 to 2012. She was a sprinter who excelled in the 200 meters and the 400.

At the Ole Miss Invitational outdoor meet in 2009, she recorded 24.48 seconds in the 200, which is the10th-fastest time in her school’s history, reports said. She also ran a 55.01 in the outdoor 400 in 2009, which still stands as the sixth-best time for the Commodores.

Her name is also listed among the top indoor finishing times for the school.

She moved on from track and became a lawyer, earning her degree from Thurgood Marshall School of Law at Texas Southern University, reports said.

She started her legal career as an intern for the NAACP and moved on to become a trial attorney for Ben & Abbott Associates in Garland, Texas.

Most recently she worked as an associate attorney at the Bassett Firm in the Dallas area, reports said.

School officials who remembered Hill from her time at the school said they were devastated by the news.

“It’s difficult for me to process the tragic news of the death of Teegan and her sister, Troinee,” Vanderbilt athletics director Candice Storey Lee said on Twitter. “I remember Teegan’s talent on the track, but even more so as a sweet and kind woman. Our hearts go out to her family, teammates and all who loved her. She’s forever a Commodore.”

Mike H. Bassett, attorney with The Bassett Firm, where Hill worked, also released a statement, according to reports.

“Teegan J. Hill was a gifted attorney and a blessing to all that knew her. She truly was a “one of a kind.” The Bassett Firm is saddened by the tragic loss of Teegan and her sister. We are praying for all of their family and friends during this very difficult time.”

Broom worked as a kindergarten teacher in the Dallas area.