Taylor Corbino spoke exclusively to ABC News about the terrifying moment the boat slammed head-on into another on Saturday.
The recent college graduate said she has no idea what caused the deadly crash, and is just counting herself lucky to be alive.
RELATED: 9 injured, 4 missing after boats collide on Colorado River north of Lake Havasu
"I can't tell you exactly what happened 'cause I don't even know," Corbino said. "I was actually sitting in the front of the boat with a friend, and he moved to the back. And he actually ended up staying back there, and they all told me to come back. Thank God I went back.
"We were actually sitting there, I sat next to my friend. We were looking at each other," she continued. "We were actually talking, and then all of a sudden, I hear, excuse my language, I hear, 'Oh s---.' And I look up and next I see the boat, the other boat. And next thing you know, I'm in the water."
Her father, Pat Kelly, on a nearby boat, said a beautiful Labor Day weekend "went to hell" in an instant as he desperately tried to save his daughter and the other passengers.
"Sounded like a freight train hitting the side of a building," Kelly said. "It was -- it was horrible. So that's when we went over to it, and we knew what happened."
Corbino said no one on her boat -- all family friends -- sensed anything was wrong before it slammed into the other craft.
"I can't tell you how long I was underwater, but I know that it was long enough to where I couldn't hold my breath anymore," she said. "I actually breathed in some water and all I told myself was, 'Taylor, swim to the top to get some air in.' I swam to the top and my friend that I was actually sitting next to on the boat, I felt him grab me."
Her father was shouting for her through the chaos.
"When it crashed, we were just trying to find her, find anybody, screaming, pandemonium," Kelly said. "Yeah, it was total chaos."
Corbino described the moment she thought her life was over.
"I thought I was going to die, yes," she said. "I thought I was going to drown."
All six people on their friends' boat survived the accident, they said. Corbino said two days later she is still sore, but otherwise fine.
"We haven't talked about it too much," Corbino said. "I think we're all still in shock. It hasn't hit us yet completely. It's been a very crazy weekend. But when I do talk to 'em about it -- we're all very thankful and blessed to be alive. We shouldn't be alive."
The incident happened Saturday near Moabi Regional Park on a stretch of the Colorado River between Pirates Cove and the Topock Marina just north of Lake Havasu. A recreational boat carrying 10 people and another vessel with six people on board collided head-on.
The Mohave County Sheriff's Department said more than a dozen people on-board the boats were thrown into the water.
The body of California resident Chrisi Lewis was found Monday morning. Lewis was from Visalia, according to ABC7 sister station KFSN-TV. She worked as a nurse and was also the step-daughter of a former sheriff in Tulare County.
One of the missing people was identified as Brian Grabowski, 49, also of Tulare County. KFSN-TV reports that Grabowski's wife was rescued following the boat crash and was transported to a Las Vegas hospital, where she is recovering from injuries.
Family members identified another missing boater as Kirra Drury. Loved ones created a GoFundMe account to help Drury's family search for her.
Dive teams are also looking for Reagan Heitzig. A dive team from the Los Angeles County Sheriff's Department is helping with the search of all three victims.
In the immediate aftermath of the impact, good Samaritans in passing boats pulled crash victims out of the water. Nine people were hurt -- two of them critically.
It's believed none of the boaters were wearing life vests at the time.
The exact cause of the crash remains under investigation.
ABC News' Bill Cunningham and Suzanne Yeo contributed to this report, as well as KFSN-TV.