Mario Garcia and son-in-law Nivardo De La Torre had been killing time while waiting for their wives, police say.
They ended up finding Matthew Reum, 27, of Mishawaka, whose truck had crashed off Interstate 94 on 20 December.
In hospital, Mr Reum had one of his legs amputated and is now in intensive care, his union says.
Mr Garcia said he had seen the wrecked truck and was moving an airbag out of the way when Mr Reum “woke up”.
The driver told the men he had been trapped and pinned in his seat under the bridge near Portage, he recalled at a news conference held by the state police.
“He tried yelling and screaming, but nobody would hear him,” Mr Garcia recalled the man telling him.
“It was just quiet - just the sound of the water.”
Mr Reum, a union welder, had had no food but survived by drinking rain water.
I don’t have the links right now but I’ve read numerous stories where a person was found dead in their house after they had died years ago. Many people have no one in their life. And many bosses won’t care if you stop showing up. They’ll just assume you quit.