Naya Rivera 'Mustered Enough Energy' to Get Son on Boat but 'Not Enough to Save Herself': Police

Naya Rivera's final moments were spent saving the person she loved most, according to investigators.

On Monday, the former Glee star's body was found five days after she went missing during a boating trip at Lake Piru in Ventura County, California, with her 4-year-old son, Josey, whom she shares with ex-husband Ryan Dorsey.

At a news conference Monday afternoon, Ventura County Sheriff Bill Ayub recounted what Josey told authorities about the tragic accident.

"We know from speaking with her son, that he and Naya swam in the lake together at some point during their journey. It was during that time that her son described being helped into the boat by Naya, who boosted him onto the deck from behind," the sheriff said. "He told investigators that he looked back and saw her disappear under the surface of the water."

RELATED: Glee Star Naya Rivera Dead at 33 After Disappearing on Boating Trip with 4-Year-Old Son

Ayub said that "there are a lot of currents on the lake that appear particularly in the afternoon" and that authorities believe she disappeared in the "mid-afternoon."

"The idea perhaps being that the boat started drifting, it was unanchored, and that she mustered enough energy to get her son back onto the boat, but not enough to save herself," Ayub said.

The sheriff added that there is no evidence of foul play or suicide. An autopsy will be performed at the Ventura County Medical Examiner’s Office, and Rivera will be officially identified based on dental records.

Last Wednesday, Rivera, 33, was declared missing after an outing on the lake with her son, who was found asleep and alone on the pontoon after the boat was overdue for its return.

"Naya’s son was later found asleep on the boat, which was adrift in a northern portion of the lake known as 'The Narrows' ... when a leasing agent searched for the watercraft, which was overdue with return. The young boy was wearing a life vest when he was found, and he was wrapped in a towel," Ayub said during the news conference.

"An adult size life vest was found on the boat. Several witnesses who were at the lake that day have been identified and interviewed by sheriffs and investigators," Ayub added. "There were three other rental boats on the lake that day. All of the people in those boats have been identified and interviewed. They had seen Naya’s boat at different times and at several different locations while she was out on the lake."

RELATED: Heather Morris and Other Glee Stars Gather at the Lake Where Naya Rivera Died

An extensive, five-day search at the lake began for Rivera, who was presumed dead on Thursday.

Lake Piru has been the site of several drownings over the years, and the actress's disappearance prompted a petition calling for signs warning swimmers of its dangerous conditions. Ayub noted that "swimming is allowed" in the waters.

Authorities "utilized dozens of personnel: watercraft, helicopters, with unmanned aerial systems, and on the shore, conducting a methodical and comprehensive search," Ayub said.

After a multi-day search, "today our search teams have recovered a body in the lake," Ayub told reporters. "Based on the location that the body was found, physical characteristics of the body, clothing found on the body, and physical condition of the body, as well as the absence of any other persons reported missing in the area, we are confident that the body we found is that of Naya Rivera."

He continued: "She was found in a northeastern portion of the lake, near the surface of the water. Depth of the water is between 35 and 60-feet deep, there is heavy brush and trees on the lakebed there."

In the days leading up to finding Rivera's body, her family, ex-husband and former castmates were seen visiting the lake.

RELATED: Naya Rivera Posted a Touching Photo with Her Son Days Before Disappearance: 'Just the Two of Us'

During the news conference, Ayub expressed his condolences to the actress' loved ones during this heartbreaking time.

"As you can imagine, it has been an extremely difficult time for her family throughout this ordeal, as fathers, mothers, sons and daughters, our hearts are with them and we share in their grief for Naya’s loss. We have been in direct contact with the family throughout this entire time, and we’ve kept them updated on the progress of our search efforts throughout," he said. "Our hearts also go out to Naya’s many friends and fans, who have been holding out hope for the best over the last few days."