More than 30 people were rescued or had to swim to safety when an amphibious tour bus sank in Liverpool's Albert Dock on Saturday.
A number of people were taken to hospital after the Yellow Duckmarine vessel went under just before 4pm. A "multi-agency investigation" has been launched into the sinking.
A rescue operation involving police, ambulance, coastguard and the RAF was mounted by the emergency services and 31 people were helped out of the water. Of those, 17 were taken to the Royal Liverpool Hospital for treatment, mostly for shock, but all were well enough to be discharged. No one was trapped inside the vessel, the fire service said.
The company runs tours on the city's roads with the promise of a "splashdown" ending.
It is the second time in three months that one of the yellow vehicles has sunk.
It is understood that 28 people were led to safety from the bus, including a baby whose mother held her above the water on the roof of the sinking craft. Three more were pulled from the water by firefighters.
A spokesman for Merseyside Police said everyone had been accounted for.
Eyewitnesses reported seeing a large number of people swimming in the Mersey as the vessel, one of four in the company's fleet, sank in Salthouse Dock, part of the Albert Dock complex.
People could be seen throwing life-rings into the water to help those trying to escape.
In March, the entire fleet was ordered out of the water after a bus sank, with no passengers on board. In May, the Queen and Prince Philip travelled on one of the buses when they visited the region as part of her Diamond Jubilee tour.
Writing on Twitter, the mayor of Liverpool, Joe Anderson, refused to be drawn on the future of the vessels until he knew everyone involved in the latest incident was safe.
He wrote: "Albert Dock Duck incident, look I will not make any official comment on future of these ducks until we know people are all ok+accounted for."
Anderson later tweeted: "Albert Dock incident: police confirm 31 people entered the dock, 31 people have been accounted for. Everyone ok, some people still in hospital."
The Liverpool Echo reported that Pearlwild Ltd, which operates the fleet, faces a separate investigation by the North West Traffic Commissioner, with a public inquiry set to be held later this month amid concerns over the operation of the fleet of wartime vehicles.
Chief fire officer Dan Stephens said: "Three people have been rescued by firefighters from the water. We have had assistance from a number of agencies on scene.
"Firefighters wearing dry suits and with a safety rope attached to them entered the water and swam to rescue three adults who were in the water. They brought them to safety.
"The firefighters then swam back out to check no one was inside the vessel.
"The search and rescue team, based at Croxteth Community Fire Station, also used an underwater camera to check no one was in the vessel. The vessel was in the water around 25 metres from the dock entry ramp where it enters the water."
