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, an inlet off the East River, just after 10:30 p.m. Friday.
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.
Several of the victims' family members visited the scene Saturday morning. The sobbing stepmother of one was comforted by police.
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. Then then flipped it back on its wheels and prepared to tow it away.
Police divers helping with the towing operation were hosed off by firefighters when they emerged from the creek.
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 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.
The Steinway piano factory that gives the creek its name is a few hundred yards from the crash site.