The California Highway Patrol is investigating the matter as an accident, officials said.
"We have located a decedent inside the vehicle. We believe it is our missing person," Nevada County Sheriff Shannan Moon told reporters. "We have not been able to positive identify [the victim], but it’s more than likely where we are today."
The teen's family on Monday thanked law enforcement, volunteers and everyone who helped support them.
“While we accept this sadness cast under death’s shadow, the rising sun shines light upon us, reminding us not to mourn our loss, but to celebrate Kiely’s spirit and the gift that we all received in knowing her,” her family said in a statement. “Kiely will surely remain with us even though we will not get her back.”
Television news crews captured video Sunday of what appeared to be a silver SUV being pulled from the water.
Searchers had been looking for Rodni, 16, and her car, a silver 2013 Honda CRV, for weeks.
Volunteer searchers shared video of the submerged SUV on Monday, appearing to show a California license plate that matches the one on Rodni’s SUV.
Before the volunteer crew arrived, divers and swimmers — affiliated with local law enforcement agencies and armed with sonar and other equipment — didn’t detect the car that was found Sunday.
Nevada County Sheriff’s Capt. Sam Brown said his agency will be taking a closer look at any possible shortcomings of their search.
“That’s a great question. That’s one that everyone is going to have, right, ‘How did we not find it while we were searching?'" Brown said.
Rodni was last seen Aug. 6, along with hundreds of other partying teens, at the nearby Prosser Family Campground, in an area known as "The Sanctuary" in Truckee.
She vanished, and authorities initially worried that their search was slowed because witnesses may have hesitated to come forward because of possible underage drinking.
Early reports cast Rodni’s disappearance, incorrectly, as a possible abduction, Brown said.
Brown added the miscommunication may have inadvertently helped the investigation.
"We also probably wouldn’t have received all the services and all the people if [a possible kidnapping] wasn’t an option," he said. "If this was truly a search-and-rescue mission, we may not have had all the resources to conduct interviews.”
An autopsy is set for Tuesday.
Adventures With Purpose thanked local law enforcement Monday for allowing it to join the search.
The divers plan to take their equipment this week to Selma, California, in hope of finding Jolissa Fuentes, 22, who hasn't been seen since Aug. 6.
The team also hopes to assist San Luis Obispo law enforcement officers in their search for Annette Adams, who was last heard from on April 25.
“Hug your loved ones a little tighter. Take the time to take time, as we never know when it’ll be our last opportunity to do so. I hope, as tragic as this outcome turned out to be, that this will carry on so that we are able to help the next family we did here," diver Nick Rinn said.