Former "Glee" star Naya Rivera is presumed to have drowned while boating on a lake near Los Angeles, authorities said on Thursday, but no body had been found almost 24 hours after she was last seen.

Rivera, 33, who played high school cheerleader Santana Lopez in the television series until 2015, went missing on Wednesday after renting a boat on Lake Piru with her four-year-old son Josey.

"We are presuming that an accident happened and that she drowned in the lake," Ventura Country Sheriff's spokesman Chris Dyer said on Thursday.

Rivera's son was found alone and sleeping in a drifting boat on Wednesday and told authorities they had both gone swimming but his mother never returned. Lake Piru is a recreational reservoir about 50 miles north of downtown Los Angeles.

Officials said there was no indication of foul play but it was too soon to say what happened, or how long it might take to find Rivera's body.

"If the body is entangled in something beneath the water it may never come back up," Sgt. Kevin Donoghue told reporters. "This is a terrible tragedy for all of them," he added, extending condolences to Rivera's family.

Donoghue said visibility in the 30 foot (9 meter) deep area where the boat was found was poor for divers, with multiple trees and plants underwater.

More than 100 people were involved in the search that also included helicopters and boats. Donoghue said the search would continue until nightfall and resume on Friday.

"Glee," the television musical drama about a high school choir, was one of the biggest pop culture hits 10 years ago but has seen its share of tragedy.

Actor Cory Monteith, who played football player Finn, died of a drug overdose in 2013, and Mark Salling, who played Puck, killed himself in 2018 after pleading guilty to possessing child pornography.