No one was hurt.
The Coast Guard says the boat sustained no major damage and initial indications are that drugs or alcohol were not a factor in the accident. The boat's operator says ice may have moved or obscured the marker buoys, knocking the ferry off course.
The ferry, called The Finest, went aground on a sandbar in 4 1/2 feet of water at about 7 p.m. ET, said Lionel Bryant, a Coast Guard chief warrant officer. It was between 600 and 800 yards offshore.
Five hours later, the incoming tide freed the boat.
"It refloated and is under its own power," Bryant said.
A man who suffered an allergic reaction was taken by helicopter to a hospital were he was in stable condition, a hospital spokeswoman said.
The Finest, owned by New York Fast Ferry Corp., was taking commuters from Manhattan to a marina in Atlantic Highlands, about 18 miles away.
Passengers said they remained warm and comfortable as they waited to leave the boat.
"They gave us free beer, for a while. We also had snacks, like peanuts," said Grayson Sanders, who has been taking the ferry home for the past six months.