Missing Glee star Naya Rivera is now presumed dead, police said.
The Ventura County Sheriff’s office said the effort to find the actress is now a “search and recovery operation”.
There is no foul play suspected and officers believe Rivera, 33, drowned.
She went missing on Wednesday while on a rented boat with her four-year-old son at Lake Piru, about 56 miles north-west of central Los Angeles.
Police said a huge search operation was launched, but the actress was not found.
It resumed on Thursday morning and officers gave a grim update shortly afterwards.
Officer Chris Dyer said: “The latest is that we’re switching efforts into a search and recovery operation.
"That doesn’t change anything in the efforts that we’re putting forth to locate her but it changes the title, in a sense.
“We’re presuming that an accident happened, we’re presuming that she drowned in the lake.
"There are no signs of foul play, no signs that anything went wrong besides a tragic accident.”
Mr Dyer added: “The goal is still to bring Ms Rivera home to her family so they can have some closure.”
The alarm was raised after Rivera, best known for playing high school cheerleader Santana Lopez on musical comedy series Glee, failed to return the boat, which was found drifting with the child sleeping alone on board.
The search for Rivera resumed at daybreak on Thursday, with helicopters, boats, divers and sonar teams expected to be involved.
The lake varies in depth greatly, Mr Dyer said, saying it can go from between 50-60ft to 4ft over a short distance.
Visibility in the lake during the daytime is about eight to 10 inches, while sizeable debris including trees flow beneath the surface, Mr Dyer said.
Rivera had visited the popular lake previously, the police said. The focus of the search is the northern end of the lake.
Rivera’s son, Josey Hollis, is in good health and with family, police said.
He told officers his mother put him back on the boat but never got back on herself.
On Tuesday, Rivera tweeted a picture with her son, captioned: “Just the two of us.”
The actress earned significant success starring in Glee and the California-born star followed it up with her feature film debut in 2014 horror film At The Devil’s Door.
She later had a role in the Lifetime TV series Devious Maids.
Rivera became engaged to rapper Big Sean in October 2013, but they ended their relationship in April 2014.
She then began dating actor Ryan Dorsey and they married in Mexico in July that year.
The couple had son Josey Hollis in September 2015.
Rivera filed for divorce after two years of marriage, but they later called off the separation before finalising their divorce in June 2018.
Pop star Demi Lovato and Rivera’s former Glee co-stars were among those sharing their hopes for her safe return on social media.