The search for two passengers who went missing after the "Duck" boat collided with the barge has been called off.

(CNN) -- The body of a young female was recovered near the site of a boat accident in the Delaware River, Philadelphia, Pennsylvania police told CNN Friday morning.

The unidentified remains are currently being transported to the Philadelphia medical examiner's office, Officer Christine O'Brien said.

The Coast Guard will not say definitively that the person was a victim of the accident until the body is positively identified by the medical examiner.

Two passengers -- a 16-year-old girl and a 20-year-old man -- went missing in that area after a tour boat collided with a barge on the Delaware River in Philadelphia on Wednesday.

Rescuers saved 35 people who were on the so-called duck boat at the time of the crash.

The tour boat had a clean record, said the president of Ride the Ducks, who traveled to Philadelphia from the company's headquarters in Norcross, Georgia.

"I can tell you this boat has been inspected frequently. Twice daily. We've never had a problem with this boat," said Chris Herschend.

The company voluntarily shut down its nationwide operations, including Stone Mountain Park, Georgia; Branson, Missouri; and San Francisco, California. "What we hope to learn [is how] to prevent this from ever happening again," Herschend said.

Officials said people reacted quickly after the collision.

"The immediate response was amazing," said U.S. Coast Guard Capt. Todd Gaitlin. "The private citizens helped [rescuers] get people out of the water."

Police and Coast Guard vessels searched the river Thursday.

Lt. Frank Vanore of the Philadelphia Police Department told reporters Wednesday that the boat had "mechanical trouble" and the engine shut down after a fire on board. While the boat was in the river and waiting for help, it was hit by a barge, he said. The boat overturned and passengers were spilled into the river.

National Transportation Safety Board officials will interview crew members on Friday, NTSB spokesman Robert Sumwalt said in Philadelphia Thursday afternoon.

The investigation will include reviews from cameras along the river, training and navigation methods and safety equipment.

"We want to find out what happened and issue safety regulations so that this does not happen again," said Sumwalt, who is vice chairman of the NTSB.

Alcohol tests on crew members came back negative, Sumwalt said. Drug tests will take longer to analyze. The 10 investigators will also look at allegations that similar boats have previously overheated or had mechanical problems.

Herschend said the company is investigating and assisting fire and police officials.

"I believe this was an accident."

He said he could not speculate on whether there was a fire onboard or how the boat's captain communicated during the incident. But he said he believes the unidentified captain followed all procedures. He was unsure how long the boat was dead in the water before the collision.

Asked by reporters Thursday whether the barge was at fault, Herschend said, "I don't want to speculate. For me it is not to assign blame."

He said the 10-year-old craft had portable flotation devices.

Herschend said the company is checking on whether the captain told people to jump off the boat moments before impact. "It is my expectation for the captain that he followed our emergency procedures to the letter," he said.

"Our first priority is the people on board," Herschend said. "Then we are going to work on making sure this never happens again."

The missing people are believed to be from outside the United States, he said.

Searchers located the boat in about 50 feet of murky water, but it was too dangerous to send divers down, said William Blackburn, deputy commissioner of the Philadelphia police. The boat is upright on the bottom of the river, Blackburn said.

The duck boats are amphibious military vehicles designed in the 1940s.

The NTSB will also conduct a 72-hour history to determine the mental and emotional state of the crew of boat vessels, Sumwalt said.

Eleven passengers were hospitalized. Nine were released by Thursday morning. One passenger suffered a broken jaw, Gaitlin said.

The company, Ride the Ducks, is owned by Herschend Family Entertainment.

The company's website posted this message Thursday: "Our thoughts and prayers are with our Philadelphia tour guests, crew members and their families. We are attending to their needs first. In the interim, we have voluntarily suspended our Ride The Ducks operations nationwide. If you already have a reservation, you can receive a full refund or reschedule for a future date. We will resume operations shortly."

Source: http://cnn.com