Naya Rivera's body "may never come back up", police have said

He said: "If the body is entangled on something beneath the water, it may never come back up.

"There's no way to really say. We're putting our best foot forward to try and locate her, we're using all the assets that are available to us including technology like sonar."

But he insisted the police are doing "everything [they] can" to find the 'Glee' star.

He added: "We're relying on their expertise to help us in that endeavour. We're going to do everything that we can to find her."

Naya's fellow 'Glee' star Heather Morris is "holding onto hope" that her friend will be brought home "in a swift and speedy recovery".

She told E!: "It's so hard to wrap your head around something unknown.

"I'm holding on to hope that the rescuers will bring Naya home in a swift and speedy recovery. I know she would remind me in moments like this that God has a plan for everything and although we may not know that that plan is, we need to keep our chin up and stay strong."

Naya's son was found sleeping on the boat when the vessel was discovered, but she was nowhere to be seen.

Divers have had difficulty seeing in the water, which has made the operation a "slow process".

A police report from the Ventura County Sheriff's Department reads: "The search for a missing Los Angeles actress at Lake Piru has turned into a recovery mission as of Thursday morning.

"Naya Rivera rented a boat at the lake Wednesday afternoon and went for an excursion with her four-year-old son. The boat was found drifting in the northern portion of the lake with the child alone and asleep onboard. Rivera's son told investigators that he and his mother had been swimming in the lake, and he got back in the boat, but Rivera did not.

"Approximately 50 sheriff's personnel, along with a helicopter, boat crews, divers, and unmanned aerial vehicles searched the lake for five hours Wednesday evening, but Rivera could not be found. The entire shoreline and surface of the lake were thoroughly searched. Divers also searched under water in the area where the boat had last been seen. However, there was no sign of Rivera. The search was suspended at 10:00 pm Wednesday night due to zero visibility in the water and dangerous conditions for the divers.

"The search resumed Thursday morning with divers experiencing less than one foot of visibility in the water in daylight. The difficult conditions have made the recovery operation a very slow process. The Los Angeles County Sheriff's Department is assisting in the search with divers and sonar equipment. Approximately 100 personnel are participating in the mission on Thursday, including resources from neighbouring counties and the United States Coast Guard.

"Investigators believe Rivera drowned in what appears to be a tragic accident."

More than 80 people are involved in the search after the police deployed "helicopters, boats, and ATV vehicles".