SAN BERNARDINO (CBSLA.com) — A 4-year-old boy drowned in a spa pool Friday in San Bernardino.

Investigators said the victim was playing in a backyard spa pool, located at a home in the 2600 block of Mercedes Drive, when one of his hands got caught in a suction drain.

READ MORE: FBI Offers $20K Reward For Couple Who Went On The Run After Being Convicted In COVID-19 Relief Fraud Scheme

Fire officials told KCAL9’s Rachel Kim that the boy’s great-grandparents were watching him and tried to rescue the child.

“When crews arrived on scene, they found the grandfather holding the boy, actually trying to actively pull him out,” San Bernardino City Fire Department Capt. Jason Buchanan said.

It’s unclear how long the boy was underwater, but a firefighter was able to forcefully pull him out.

They performed CPR and took him to the hospital, where he later died.

READ MORE: Brush Fire Burning Near 5 Freeway In Pyramid Lake Area

“It’s just a tragic accident that could be completely avoided,” Buchanan said.

Police are now investigating how the incident happened. They said they found that the drain cover was off.

“The boy might have uncovered it himself or by pulling we might have ripped it off, but after the scene, after they took him away, they found the drain cover was at the bottom,” Buchanan said.

Buchanan said the victim is the fourth child drowning in San Bernardino so far this year. He wants parents and anyone supervising children to check the drain covers.

“Definitely make sure they’re tightened down, make sure they’re fastened, they’re not loose. That way they won’t come up when the kids are playing and they don’t get their hands or arms stuck inside,” Buchanan said.

MORE NEWS: Antelope Valley Fair Cancelled Due To Logistics Of COVID-19 Safety Protocols

Criminal charges will not be filed against the boy’s great-grandparents.