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A search and recovery effort is underway in Ventura County Thursday for missing actress Naya Rivera, who disappeared during a boat trip with her son on Lake Piru a day earlier.

Rivera, 33, was last seen on a pontoon boat she rented from a lake employee Wednesday afternoon, Ventura County Sheriff’s Office Deputy Chris Dyer said during a news conference Thursday morning.

A search began for Rivera around 4:30 p.m. when she was late returning the boat, which was rented for a three-hour period starting 1 p.m., Sgt. Kevin Donoghue said at an afternoon news conference.

“The concession workers that are responsible for renting the boats went out looking for her and that’s when they found the boat and placed a call to 911,” he said. The 911 call was later released by sheriff’s department. Deputies had said Wednesday that they received the call around 6 p.m.

The boat was found drifting on the northern end of the lake, with Rivera’s 4-year-old son asleep onboard, officials said.

The boy was wearing a life jacket when he was found, and another adult life vest was found on the boat.

The child is “healthy and fine,” and is now with family members, Dyer said.

The boy told investigators he went swimming with his mom while they were out on the lake but she never got back on the boat.

Surveillance video released by the Sheriff’s Office shows Rivera and her son arriving at the lake in a black SUV. They can then be seen walking down the dock and getting into a pontoon boat, just the two of them, and departing north into an apparently unoccupied lake. Only three other vehicles and a golf cart are visible in the parking lot.

Rescue divers were called to search for Rivera but efforts were called off when it got dark Wednesday night.

“We’ve had no indication, after talking to her son, that Miss Rivera made it to shore,” Donoghue said. “So the focus of our search efforts are in water at this time.”

Investigators have found nothing suspicious at this point and are viewing the incident as a tragic accident, Dyer said. Sheriff’s officials said Wednesday that Rivera is presumed dead.

Divers returned to the water early Thursday morning, but the mode was changed to a search and recovery effort a short time later.

Changing the mode does not change the efforts of the search crews, Dyer said. “The goal is still to bring Miss Rivera home to her family so they can have some closure,” he said.

Since the search started Thursday morning, manpower was increased to over 100 personnel on-site actively searching, Donoghue said. At least six boats and two helicopters were also being utilized.

Search teams would continue operations until night fall and would resume at daybreak Friday, Donoghue said.

“One of the things that complicates the search is we have to go with where the boat was found initially, and then work our way outward from there,” Donoghue said. “And we’re talking about underwater and visibility that’s really limited. It’s a slow going search process.”

Rivera had been boating at Lake Piru before, according to Donoghue.

The actress is best known for her role on the TV show “Glee,” where she played cheerleader Santana Lopez. Rivera also had roles on “The Bernie Mac Show” and “Devious Maids.”

Lake Piru is closed amid the search for Rivera, sheriff’s officials said. The reservoir is located about 40 miles northwest of downtown Los Angeles at the edge of Los Padres National Forest.