Gene Opheim, 58, and his son, Austin Opheim, 32, were pulled from the manure pit Saturday afternoon, but were later both pronounced dead at a nearby hospital.

Police say that when Austin went to retrieve equipment that had fallen into the pit he was overwhelmed by the combination of hydrogen sulfide, methane, ammonia, and carbon dioxide that the manure releases when disturbed. 

When his father went to rescue him, he too fell victim to the gases. 

“(Gene) was carrying Austin on his back and bringing him up and he got almost to the top and he got overcome, and down they went,” Palo Alto County Sheriff Lynn Shulte told the Des Moines Register. 

On July 7, two Wisconsin hog farmers, also father and son, were killed in almost identical circumstances. 

In 2007, a similar incident took the lives of four members of a Virginia family, as well as a farm worker, who were trying to save one another from a dairy farm’s manure pit.