PORTAGE, Ind. (CBS) -- Matt Reum survived nearly a week in the wild on nothing but rainwater, as he was.
CBS 2's Lauren Victory got her hands on the 911 call made by one of the two fishermen who found the crash victim.
As they explained at a news conference on Tuesday, Mario Garcia and his son-in-law Nivardo Delatorre, were walking along Salt Creek near Portage, Indiana, in search of a good fishing spot Tuesday afternoon. But something shiny caught their attention – and it turned out to be a mangled truck.
Garcia said he moved the white airbag in the cab of the truck and went to touch what he thought was the driver's dead body. But the driver turned around, and began speaking.
"It almost killed me there, because it was kind of shocking," Garcia said Tuesday night, "but he was alive, and he was very happy to see us. Like he was really like, I've never seen a relief like that."
The astonishment could be heard in Delatorre's voice as made the 911 call.
"Hey sir. I'm, I'm here at… let's see, a fishing hole right off of the expressway here," Delatorre told a 911 operator. "I can't really - I don't know the address, but there's a car that's been here since Wednesday, and there is a person inside of it. He's still alive too."
The fishermen could not believe this all happened as they went out on a leisurely mission to find a fishing spot.
"Dude, that's crazy," Delatorre said in the 911 call. "I came down here to check for fishing and he's down here in the car."
While Reum was alive, he was in shock.
"You guys might need the jaws of life to open the doors," Delatorre told the 911 operator. "His truck is pretty wrecked."
On the call, Delatorre was heard yelling to the victim while on the phone.
"They're on their way, buddy!" Delatorre was heard saying. "They're on their way!"
As Delatorre predicted, rescue crews did have to bring in the jaws of life to get Reum, 27, out of the truck. The vehicle had gone off Interstate 94 and had rolled underneath a bridge back on Wednesday, Dec. 20.
Reum spent six days – including Christmas Eve and Christmas Day – trapped in the wrecked truck out in the elements before someone found him. We are told Reum couldn't call for help because his cellphone was just out of reach.
On Wednesday, friends posted a picture of Reum smiling and giving a thumbs-up from his hospital bed. They have started an online fundraiser for Reum – a welder and a member of the member of Boilermakers Local 374 who lives in Mishawaka, Indiana, near South Bend.
Multiple sources described him as kind, respectful man.
We are told that as of Wednesday, Reum was awake and able to speak.
Reum told the fishermen who rescued him that he survived off rainwater. CBS 2 tapped two independent medical experts to understand more about the odds of surviving so long in the elements while trapped – with only rainwater to drink.
"This man was very, very lucky," said Dr. Dr. Emily Jameyfield of the University of Chicago Medicine emergency department.
The experts explained that people can't survive very long without water.
"You can survive weeks to months without food – without solid food - but you can only go a handful of days, if even, without water," said Jameyfield.
"People can survive longer without food than they can without water," said Dr. Evelyn Huang, an emergency medicine physician at Northwestern Memorial Hospital, "the reason being is that there are stores of energy inside of our body that can replace food, but water is really hard to access and really hard to store."
Victory asked Huang to explain in junior-high biology terms why the body needs water.
"Water is essential to life," Huang said. "It's essential to all most mammal lives."
As the Mayo Clinic explains, water amounts to 60 percent of a human being's body weight.
It is needed for multiple functions that are necessary for survival – including regulating body temperature; moistening tissue in the eyes, nose, and mouth; protecting internal organs and tissues; carrying oxygen and nutrients to cells; keeping joints lubricated; flushing out waste products and lessening the burden on the kidneys and liver; and dissolving minerals and nutrients so the body can access them, the Mayo Clinic explained.
Doctors amputated Reum's left leg at mid-shin earlier Wednesday. Friends said Reum broke several bones, and will need some time to recover physically and mentally.
He remained in critical condition as of early Wednesday evening.
Late Wednesday, Reum released a statement through a hospital spokesperson. He said he is requesting privacy while he heals – and he is grateful for all the support he has received.
Reum's friends said he needs a couple of days to process what happened before he reveals to the world how he survived.