Naya Rivera died of accidental drowning, an autopsy into the actress' death states.
The 33-year-old American Glee star's body was found in Lake Piru in southern California yesterday, six days after she was reported missing.
Her body was located in the same area where she went missing. It was concealed by shrubbery and floated to the surface after it filled with gas due to decomposition.
The Ventura County Medical Examiner's Office said the findings from an autopsy released today determined "the cause of death is drowning and the manner of death is accident".
"The autopsy findings are consistent with a drowning and the condition of the body is consistent with the time that she was submerged," a statement from the Medical Examiner's Office said.
Rivera's 4-year-old son Josey told investigators his mother boosted him on to their rented boat after they had been swimming together before she "disappeared".
"No traumatic injuries or disease processes were identified at autopsy," the statement added.
"There is no indication from the investigation or examination that drugs or alcohol played a role in the decedent's death."
Police believe Rivera "mustered enough energy to get her son back onto the boat but not enough to save herself," Ventura County Sheriff Bill Ayub said yesterday after her body was found.
Rivera rented a pontoon boat on the lake, which lies inland 100km northeast of Los Angeles, at about 1pm last Wednesday with her son, Josey Hollis Dorsey.
The boat rental company went searching for the pair when Rivera didn't return the vessel on time, and discovered Josey asleep and adrift on-board.
"We know from speaking with her son that he and Naya swam in the lake together at some point during their journey," the sheriff said yesterday.
"It was during that time that her son described being helped into the boat by Naya who boosted him on to the deck from behind. He told investigators that he looked back and saw her disappear under the surface of the water.
"There are a lot of currents on the lake that appear particularly in the afternoon. We believe it was midafternoon when she disappeared.
"The idea being perhaps 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."
Heather Morris, who played Rivera's love interest on Glee, joined the star's family members, including her ex-husband and the father of Josey, Ryan Dorsey, at the lake yesterday as many paid tribute to their colleague on social media.
A photo shows Morris and several other Glee stars holding hands and looking out onto the lake where Rivera went missing.
"It has been an extremely difficult time for her family throughout this ordeal," the sheriff said. "Our hearts are with them and we share in their grief for Naya's loss."