Police say the suspect escaped on the water, riding away on a jet ski.
The shooting happened around 5 p.m. at the Princeton Avenue Boat Launch in the city's Tacony section.
The 30-year-old victim was found in the front seat of his white pick-up truck, with a jet ski attached.
Suspect flees on jet ski after deadly shooting at boat launch along Delaware River in Philadelphia
Philadelphia police said the victim was shot multiple times, though investigators have not determined what led to the gunfire.
"He was shot multiple times in his head and his back area. The medics pronounced him on scene," said Police Captain Timothy Stephan, with Philadelphia police.
Neighbors describe the victim as a quiet man who came to the US from Brazil with the hope of a better life for his family.
The victim's wife and several witnesses were there at the time of the shooting, but detectives are piecing information together due to a language barrier.
The male shooter remains at large, but authorities said the individual is known to witnesses.
Witnesses reportedly told police that the suspect and victim were acquainted, but no further details have been released.
A man visiting the area for the first time says it will be his last. Marcus Oliveira of Cinnaminson described the scene as "very crazy," adding, "I was back there and I saw all the lights, so I was like, something is going on."
Captain Stephan noted that extra officers were already stationed along the waterway due to heavy weekend crowds.
"We do monitor these hot zones that we have. We did have officers that were in the area as well when the calls came out. They responded promptly," he said.
Calling the violence "a shame," Stephan said police are working to keep the area safe and secure. "We are doing our best to provide a safe area to enjoy their weekends and enjoy the nice weather."
No arrests have been made.
Anyone with information can call or text Philadelphia police at 215-686-TIPS (8477) or submit an anonymous tip online.