Photo clue in search for Glee star Naya Rivera

As the search for presumed drowned actress Naya Rivera continues, it has been revealed she sent a photo to a family member from the boat she had rented with her son.

Police divers are reportedly using the photo in attempts to narrow down where she may have disappeared before her 4-year-old son was found alone, adrift on the boat they'd boarded together three hours earlier on Lake Piru.

Authorities say Rivera took the picture of Josey somewhere between 90 minutes and two hours before he was found by fellow boaters, asleep without his mother.

"There was a picture sent to a family member that showed the boy on the boat by a cove," Robert Inglis of the Ventura County Sheriff's Office Search & Rescue Team told Us Weekly on July 12 (US Time).

"We found where that cove was."

Inglis revealed the photo was a crucial starting point for their team's initial search efforts.

"We did send our dive members to those two locations and searched those extensively," Inglis told the outlet, adding that in a lot of instances, there are onlookers or witnesses "who see someone jumping off a boat so we know which area to search and we can find the body more quickly."

"In this case, it really could be the whole lake," he said.

"There are a lot of coves that have to be searched."

Authorities are confident they will locate Rivera's body, and have said the recovery operation "will continue to at least Tuesday".

The Glee star's family were united in grief on Saturday as they tried to connect with the missing actress.

Naya's mum, Yolanda Rivera, was pictured kneeling in front of Lake Piru in Ventura, California.

Naya's ex-husband, Ryan Dorsey, joined the emotional scenes, wading through the water in tears.

He was reunited with Naya's dad, George Rivera and her brother Mychal, who entered the water fully clothed in attempt to reach the missing star.

Together, the family took a boat out onto the water, joining the desperate search.

It comes after footage of the underwater hunt for Rivera was released as investigators revealed it could take up to five days to find her body.

Ventura County Sheriff's Office sergeant Kevin Donoghue told People that after speaking with Naya's 4-year-old son Josey, who was with the actress when she went missing, they have no reason to believe she took her own life.

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

The search for 33-year-old Rivera entered its fourth day on Saturday.

Ventura County Sheriff's Department shared footage of the "difficult" search for the missing actress on Twitter over the weekend.

"Here's an example of the underwater visibility at a 30-foot depth in Lake Piru," the Sheriff's Department tweeted.

As there is almost zero visibility in the lake, divers are resorting to search by feel, which means it could be several days before crews locate her body, Eric Buschow, Ventura County Sheriff's Office spokesman said at a press conference on Friday evening.

"We don't know if she's going to be found five minutes from now or five days from now, so we're still going to be continuing this effort," he said.

"The visibility in the water is one to two feet," Buschow added.

Officials are using a sonar system to hunt for her body.

"It's very effective," he said.

"They get a really detailed image and they can go down and focus on specific things rather than putting divers in the water where they're literally feeling around because they can't see."

The search has been severely hampered by the poor visibility of the lake's murky waters.

Rivera is presumed to have drowned at the southern California lake on Wednesday and a search and recovery operation has been underway for the past few days.

Naya's son, who was found alone on a rented boat, told investigators his mum "jumped into the water but didn't come back up".

Josey is now safe with family members and his father, actor Ryan Dorsey, who Naya divorced in 2018.

Search and rescue diver Robert Inglis told DailyMailTV Naya could have dived into the water from her boat and hit her head on one of the branches, shrubs and rocks beneath the surface.

25 divers are involved in the search for the her body but are being hampered by poor visibility, with the lake up to 15 metres deep in some parts.

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

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

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".