The mother and her two daughters died on Friday when water as deep as nine feet engulfed their vehicle on a low-lying section of the city's Washington Boulevard near the Allegheny River, Reuters reports.
Kimberly Griffith, 45, and her daughters Brenna, 12, and Mikaela, 8, drowned in the vehicle and were pronounced dead at the scene around 6 p.m., a spokeswoman for the Allegheny County medical examiner's office said on Saturday.
Rescue boats that responded to the area floated directly over top the car, which was completely underwater and pinned against a tree, officials said.
"The bottom of the boat didn't even scrape against the top of the car," Raymond DeMichiei, deputy director of the city Office of Emergency Management, told the Associated Press.
The body of an elderly woman was found on Saturday, the New York Daily News reports.
The water pinned their vehicle to a tree and they were unable to escape, authorities said earlier.
Rescue workers also recovered a body from the Allegheny River believed to be that of an older woman reported missing during the flood, Raymond DeMichiei, the city's deputy director of emergency management, said on Saturday.
During the flood, more than a dozen cars were stranded along the road, local media reports said, and paramedics in boats went from car to car to rescue drivers and passengers. Some motorists stood on their vehicles' roofs or clung to trees to avoid the rising water.
A severe thunderstorm that triggered the flood caused power outages in parts of the city late Friday afternoon.
Police said 18 cars were trapped in the flooding and 11 people were rescued. One was taken to a hospital.
Shocked motorists said they escaped out of their car windows after they became engulfed in the surging tide.
"The manhole covers started popping up, and it looked like the road exploded and the waters came up really fast," Tara Howes, 34, told the Tribune-Review.
"I saw people swimming on the sides of the road. It was pretty scary."