(CNN) -- The U.S. Coast Guard on Saturday released recordings of radio communications after this month's collision between a tour boat and a barge in Philadelphia, Pennsylvania.
Thirty-seven people were on board the smaller duck boat in the Delaware River on July 7 when the accident occurred. Two people, both from Hungary, were killed.
"Hey ferry, ferry, ferry! Whoa, whoa, whoa, whoa, whoa!" an unidentified voice yelled early in the incident, apparently witnessing the collision.
A tug boat then called in to a Coast Guard radio center.
"This is Freedom. We got people in the water on Penn's Landing. It looks like they got run over by a barge. One of the duck boats. I am going in to pick 'em up."
"Roger, captain. How many persons are in the water? Over."
"No idea. I don't have time to talk to you right now. I am going to get the people."
The Coast Guard radio operator then advised other vessels to assist in the search for the 37 passengers.
Duck boat crew members told investigators that they made radio calls to the tug boat Caribbean Sea that were not answered prior to the collision, the National Transportation Safety Board said earlier this month.
The Caribbean Sea was pushing the barge that collided with the tour boat, causing it to sink in 55 feet of water, the report said.
The skipper of the Caribbean Sea can be heard on the recordings, responding to a Coast Guard call.
"We are right here next to the ship Freedom. We are the ones that, I guess, capsized the duck boat. We're on scene just making sure that no one got injured or if we can help in anyway. We do have a barge alongside, so there's not too much we can do."
The Coast Guard radio person then asked him to throw any needed life jackets into the water.
One of five crew members of the Caribbean Sea invoked his Fifth Amendment right against self-incrimination and declined to meet with investigators, the safety board said earlier this month.
According to CNN affiliate WPVI, these recordings are just some of the many elements federal investigators are reviewing as they probe the circumstances surrounding the collision. They also continue to examine the structural damage of both vessels.
The tour boat, the DUKW 34, carried 35 passengers and two crew members when it experienced mechanical problems about five to 10 minutes before the crash, the NTSB report said. That problem led the ship's master to anchor the tour boat.
Meanwhile, the Caribbean Sea approached with the barge.
Around 2:36 p.m., the bow of the barge hit the small tour boat, causing it to sink, investigators said.
People who operated several vessels in the area have told federal investigators that they heard the tour boat's radio calls.
The National Traffic Safety Board said it's looking into those accounts.