As the search continues for Glee star Naya Rivera it's hoped a witness can provide clues as to what happened in the lead-up to her presumed drowning.

Rivera has been missing since Wednesday when she and her son Josey headed out on Lake Piru on a rental boat.

The 4-year-old was discovered sleeping alone on the boat hours later, reportedly telling police his mum had "jumped into the water but didn't come back up".

The search for Rivera is now a "recovery operation" and the actress is presumed dead.

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Twenty-five divers are involved in the search for the her body but are being hampered by poor visibility. The lake is up to 15 metres deep in some parts.

An online petition calling for police to "find and interview" a jetski driver that was on the lake as Rivera and her son left the dock has got more than 7000 signatures.

CCTV footage released by police shows a jetski on the lake as Naya Rivera took off from the dock. Photo / Supplied
CCTV footage released by police shows a jetski on the lake as Naya Rivera took off from the dock. Photo / Supplied

In CCTV footage released by the Ventura Country Sheriff's Office, a jetski can be seen circling on Lake Piru as Rivera and Josey take off in their boat.

The petition urges police to speak to whoever was on the jetski as if "anyone knows what happened to her it was most likely the people on the jetski".

Ventura County Sheriff Sergeant Kevin Donoghue told People on Friday that "everything that we've learned so far leads to this being some sort of water recreational accident".

To say definitively what actually happened, we really can't say. We just don't know, it's a mystery," he said.

"We're still investigating, we're still searching. We're trying to uncover clues as we go. But so far, we really don't have a lot of information to make any guesses as to what could have happened."

'Not the first, nor the last'

Rivera's disappearance has prompted locals to start a petition calling for signs warning of Lake Piru's strong currents to be installed.

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Seven people are believed to have drowned at the lake just between 1994 and 2000, according to the Los Angeles Times.

More than 22,000 people have signed the petition claiming the Glee star "is not the first, nor the last to go missing at Lake Piru".

Naya Rivera is reported missing on Lake Piru in California. Photo / Instagram@nayarivera
Naya Rivera is reported missing on Lake Piru in California. Photo / Instagram@nayarivera

Lake Piru is a very deep lake with very bad whirlpools, people have been asking for years for the city to put up warning signs for swimmers," the petition read.

"Locals of Ventura County don't go to Lake Piru for this reason! Tourist have no idea what they're getting into. Lake Piru needs signs. We're tired of waiting. We need justice for all those who got lost at Lake Piru. Put up the signs."

As well as strong currents Lake Piru has a lot of sticks and plants underwater, making the search for Rivera a slow and complex process.

Volunteer diver Max O'Brien has described the efforts to find Rivera's body as "kind of a Braille search" with divers looking "by feel".

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As well as CCTV footage, the 911 call reporting Rivera missing has also been made public.

The caller mistakenly refers to Rivera's child as a "little girl".

"The emergency is we have a missing person, we found a little girl in one of the boats by themself and the mum's nowhere to be found," the caller says.

"My husband was one of the people that was there, I'm going to find out more information, he just wanted to call it in."

Rivera's son was discovered by another boater three hours after she had rented the craft.

The star's vehicle, a black Mercedes G Wagon, was found in the car park with her handbag inside.

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Who is Naya Rivera?

• Rivera starred on Glee from 2009 to 2015 where she played Sanatana Lopez, co-captain of the Cheerios and a member of William McKinley High School's Glee Club.

• In 2013 she launched a singing career with single Sorry alongside then-fiance Big Sean, however, her career in music failed to take off.

• In 2016, she published a memoir called Sorry Not Sorry: Dreams, Mistakes, and Growing Up, which revealed real-life feuds and scandals.

• Rivera married actor Ryan Dorsey in 2014 after her engagement to Big Sean fell apart.

• Rivera and Dorsey welcomed son Josey in September 2015.

• In 2017, the actress was arrested for misdemeanour domestic battery after Dorsey claimed Rivera hit him in the head and lip while they were taking their son for a walk. The charges were later dropped and the couple split. Their divorce was finalised in 2018.

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• Rivera and Dorsey shared joint custody of their son.