Officials from the Bastrop County Sheriff's Office said three people died in Elgin, Texas, after falling into a gas-filled cistern tank that was partially filled with water.
Police said they believe one of the victims ended up in the underground tank in an attempt to rescue a dog that fell in. The sheriff's office said two other people are believed to have followed, trying to help rescue the first person who had jumped in.
A fourth person opted to return to their truck to call 911 and get assistance.
The dog died along with the three people.
Delvys Garcia, 37, Denise Martinez, 26, and Noel Vigil-Benitez, 45, were all identified as victims. All three victims are from Florida.
Bastrop County Sheriff Maurice Cook, said, "The water level is about eight feet below the ground. So now he is in a hole, eight feet below, in water that we determined had hydrogen sulfide gas in it."
"We are speculating that the hydrogen sulfide gas overcame them, and they were not able to maintain any type of buoyancy on top of the water. Therefore, they sank underneath," Cook said, according to CBS Austin.
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Police said the group was out hog hunting at 1 a.m. local time on Wednesday when they became trapped in the hole. The recovery effort was finally completed at 7:30 p.m. later that same day.
Officials said the uncovered cistern was partially filled with water and had strong fumes similar to a septic tank.
"The fumes, the stagnant water, and the instability of the cistern hampered recovery efforts and prevented first responders from initially climbing into the man-made structure," the Bastrop County Sheriff's Office wrote.
"A decision was made to ventilate the cistern by removing the hydrogen sulfide gas and then removing the water. Still, the integrity of the structure was in question. Efforts were made to dig beside the structure to allow access from the side at a level near where the three bodies had been located, but these efforts were soon abandoned since breaching the side would weaken the walls and make entry unsafe," the statement said.
Cook said investigator David Newman came in to volunteer and recover the bodies of the hunters and the dog. The Elgin Fire Department and the City of Elgin utility crews helped in the recovery.
