A Jet Skier tried to rescue his drowning pal in Brooklyn’s Gravesend Bay just after sunset last night, but his heroism was in vain — the swimmer died at a hospital, officials said.

The incident occurred at 9:15 p.m. off Bayview Avenue and West 37th Street in Coney Island, where the 37-year-old victim was at a July 4th beach party.

At dusk, the Jet Skier and his friend, who was in a dinghy, went out to watch the fireworks, police said.

But the man on the dinghy dived in for a swim after his pal headed back to shore, police said.

Minutes later, the swimmer began to struggle and screamed for help; his friend dashed back to drag him to shore.

The man died at Coney Island Hospital.

“People were still swimming because it was dusk,” said Daniel Fox, 22, of Coney Island. “It was a dramatic scene. People were crying over this situation.”