The driver escaped serious injury and told officers at the scene in the Astoria section of Queens that the four were trapped in the submerged car.
Police said the 2009 Honda Accord tumbled into Steinway Creek, a trash-strewn inlet off the East River, just after 10:30 p.m. Friday. They continued Saturday to investigate what caused the crash.
Fire department divers pulled the four victims from the car. Police identified them as 21-year-old Darius Fletcher, 19-year-old Jada Monique Butts, 19-year-old Crystal Gravely and 20-year-old Jaleel Furtado. They were pronounced dead at hospitals.
A stream of friends and family members of the victims visited the accident scene throughout the day. The sobbing stepmother of one was comforted by police.
Nineteen-year-old Indja Ruiz said she knew all the victims but was closest to Gravely. "Everyone loved and respected her," she said.
The 20-year-old driver was listed in stable condition at Elmhurst General Hospital. Police did not immediately identify him.
Police towed the car from the creek Saturday morning and placed it on the pavement, wheels up, just a few feet from the water's edge. They then flipped it back on its wheels and drove it away on a flatbed truck.
Police divers helping with the towing operation were hosed off by firefighters when they emerged from the creek, a foul-looking muddy inlet peppered with trash.
Police visited a car service business that has security cameras trained in the direction the car would have been going in hopes of learning the vehicle's speed in the seconds before it crashed.
The deaths shook residents of East Elmhurst, the working-class neighborhood of brick row houses where all four victims lived within two blocks of each other.
Susan Martinez, who lives across the street from the home of Crystal Gravely, said the four longtime friends had gone out to celebrate what would have been Gravely's 20th birthday Saturday.
"They were all friends and they went to church and they all had jobs," Martinez said. "That's how they grew up."
Martinez watched as Gravely's father stepped out of his house and walked slowly to the backyard without speaking to anyone.
"He hasn't taken it in yet - that his only child will never be back," Martinez said.
Hairdresser Sheila Ortiz said both of the young women got their hair done at her salon, and she had known them since they were little girls.
"Those kids were very happy," Ortiz said. "They were nice young kids, not troublemakers."
The crash occurred on an isolated stretch of road near parking lots and industrial buildings, adjacent to a wastewater treatment plant and not far from the Rikers Island jail.
After the car had been removed, city Department of Transportation workers placed a concrete barrier at the end of the dead-end street.
The Steinway piano factory that gives the creek its name is a few hundred yards from the crash site.