Three hog hunters from Florida are dead after they tried to rescue their dog from a hole that was filled with water and toxic gas, authorities say.

The incident happened at about 1 a.m. Wednesday near Austin, where two men and a woman were hog hunting with their dog, according to Bastrop County Sheriff Maurice Cook. After the dog fell into the hole, one of the men jumped in after it, Cook says. When neither could climb out on their own, the other two went in after them, he adds. The bodies of all three – plus the dog – were recovered on Thursday, Cook reports.

The four-foot-wide hole contained about eight feet of water and hydrogen sulfide gas, which carries a smell “similar to a septic tank,” authorities say. Experts believe the hunters were overcome by the gas, passed out, and drowned. They’ve identified the victims as 26-year-old Denise Martinez of Miami Gardens; 37-year-old Delvys Garcia of Naples; and 45-year-old Noel Vigil-Benitez of Wauchula.