Emergency crews were called just before 4 p.m. Sunday to Kelly Drive near Midvale Avenue in Fairmount Park.
When they arrived, the vehicle was already in the water.
Witnesses said some people along the river jumped into the water and helped rescue the woman.
Joseph Wentzell and two other good Samaritans desperately tried to rescue a panicked woman trapped inside the sinking vehicle.
"I didn't think it would be such a struggle," said Wentzell. "It didn't seem far. I could swim there easily, but then I couldn't open the doors."
Jasmine didn't want to give her last name but could see the driver in the front seat. She watched from the river banks in horror as the car began to sink into the Schuylkill.
"She was on her phone, she wasn't worried until she started sinking and then people started going in to save her," she said.
"I didn't want to open the front door because it was already going under water," Wentzell said. "I yelled to the woman to climb to the back. I tried to open the back, but everything was locked and couldn't be undone. I banged on the window with my hands, but couldn't break it. Another man was swimming, and couldn't break (the window), and a third man jumped in with a tire iron."
A dragon boat rowing by scooped up the female driver and the good Samaritans and took them to the shore line.
"And literally as soon as she got out, the car went under!" said Wentzell.
Police have not said if this was accidental or intentional, but witnesses said the driver deliberately drove into the water at the other end of the parking lot.
She was taken to an area hospital for evaluation.
As for Wentzell, he said he just happened to be at the right place at the right time.
"It's what anyone would do, you know really. I think that at first you think someone is going to come. That police and fire are going to come, and they weren't there and the car was obviously starting to sink.I just reacted," he said.