The situation occurred early this morning on the approach to the Sunshine Skyway Bridge, which connects St. Petersburg to Terry Ceia over Tampa Bay in the western part of the state.
A police officer, chasing a speeding driver, saw the person stop their car and toss the child -- who's roughly 5 years old -- from the bridge before driving away, St. Petersburg Police said. The driver was stopped about 30 minutes later.
Rescue crews found the girl, but they could not resuscitate her, police said. She was taken to a hospital and pronounced dead at 2:44am.
The man who threw the girl was later identified as Jon Jonchuck, 25, the girl's father. He has been charged with first-degree murder and is now booked in the Pinellas County jail.
St. Petersburg Police Department spokesperson Yolanda Fernandez said police are stunned by the incident.
"We have no idea why anybody would do something like this as to throw a child over a railing of a bridge into the water, let alone on a night like this and the temperatures and conditions that we have today," she told ABC affiliate WFTS.
The Associated Press and ABC News contributed to this report.