"Things are slowly coming a little more into focus, but I don't know if I'll ever find closure from this. I miss her every day," says George Rivera, who spoke to his daughter on the day she died

Naya Rivera was zipping around in a rented pontoon boat on a lake outside of Los Angeles with her young son Josey on the afternoon of July 8 when she reached out to her dad — George Rivera — with a FaceTime call, looking for a bit of advice.

"She would always bounce stuff off me," George, 64, tells PEOPLE in an exclusive interview for this week's issue. "And she wanted to go swimming with Josey out in the middle of the lake."

But when his eldest daughter informed him that the boat didn't have an anchor, George — who was taking a break from remodeling his home in Knoxville, Tennessee, when the call came through — instantly realized that jumping into the lake for a swim was a bad idea.  

For more from Naya Rivera's father, George, pick up the latest issue of PEOPLE, on newsstands Friday, or subscribe here

naya and george rivera
Naya Rivera and dad George Rivera
| Credit: Courtesy George Rivera

"I could see that the wind was blowing and my stomach was just cringing," recalls George, an avid boater. "I kept telling her, 'Don't get out of the boat! Don't get out of the boat! It will drift away when you're in the water.'"

After about three minutes, their FaceTime call cut out. "It was just heartbreaking," says George, who was left staring at the screenshot he snapped of his daughter in sunglasses and a baseball cap, grinning beneath the boat's canopy with a bright blue sky overhead. 

naya rivera
Naya Rivera
| Credit: Jon Kopaloff/Filmmagic

"I had this bad feeling that was just killing me," he remembers.

Within hours of that phone call, the bad feeling George had in the pit of his stomach became reality. 

geeorge rivera
George Rivera
| Credit: Yuri Hasagawa

Josey, who was 4 at the time, had been found asleep on the rented boat as it drifted on the waters of Lake Piru after his mother failed to return it. And Naya — who rose to fame playing the outspoken, gay cheerleader Santana Lopez on Fox's musical comedy series Gleewas missing

The 33-year-old actress' body was discovered floating in a remote section of the lake five days later by Ventura County search and rescue divers.  

naya and george rivera
George Rivera and Naya Rivera
| Credit: Courtesy George Rivera

Naya drowned after exhausting herself while struggling to get Josey back into the boat after the two went swimming, according to a report released by the Ventura County Medical Examiner.

Listen below to our daily podcast PEOPLE Every Day for more on PEOPLE's interview with George Rivera.

"It's still pretty much a big blur of pain almost a year later," says George, fighting back tears. "Things are slowly coming a little more into focus, but I don't know if I'll ever find closure from this. I miss her every day."