BEVERLY HILLS, CA - OCTOBER 07:  Actress Naya Rivera at Point Honors Los Angeles 2017, benefiting Point Foundation, at The Beverly Hilton Hotel on October 7, 2017 in Beverly Hills, California.  (Photo by Matt Winkelmeyer/Getty Images for Point Honors)
A look at Naya Rivera's nearly three-decade TV career
01:11 - Source: CNN
CNN  — 

Authorities are using sonar equipment and a specially-trained dog to search for “Glee” actress Naya Rivera in murky waters, saying the recovery operation could take days.

Rivera, 33, vanished Wednesday from Lake Piru in Southern California’s Ventura County. She went to the lake that afternoon and rented a pontoon boat with her 4-year-old son, according to authorities.

Rivera’s son was on the boat, but she was nowhere to be found. One life jacket was found on the boat and the boy was wearing another. Investigators found Rivera’s purse and her identification, but no other clues on the boat. Rivera has been presumed dead.

The lake remains closed to the public while the search continues.

“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,” said Capt. Eric Buschow, Ventura County Sheriff’s Office spokesman.

The Sheriff’s Office has teamed up with the Coast Guard and Tulare County searchers in the recovery effort. Investigators are using side-scanning sonar in water with visibility of only about a foot, Buschow said. A specially-trained dog is also being used in the search. The dog is trained to sniff just above the surface and alert handlers if they sense a body beneath the water.

The sonar equipment presented a couple images of interest during Thursday night’s search. Those areas have been searched, but nothing has been found.

Lake Piru is the result of a canyon that was dammed and flooded. It is about 2 miles long and about 130 feet deep at its deepest point.

“There is a flow to this lake,” Buschow said. “Even with that current, wherever she went down, they’re confident that that’s where she will be found.”

A plan to drop the level of the lake is planned for next month in order to do seismic retrofitting of the dam. That plan was in place well before Rivera’s disappearance, according to Buschow.

Detectives have spoken to Rivera’s son and as a result of that conversation do not believe Rivera made it to shore, he said.

Rivera played Santana Lopez on the Fox show “Glee” for six years between 2009 and 2015, and appeared in nearly every episode of the musical-comedy-drama. She was also on the CBS sitcom “The Royal Family” and in the comedy film “The Master of Disguise.”

CNN’s Faith Karimi, Dakin Andone and Stella Chan contributed to this report.