Even before a duck boat crashed into a charter bus in Seattle, killing four international students, calls had emerged for greater oversight or even a ban on the military-style vehicles that allow tourists to see cities by road and water.
Critics say the large amphibious vehicles are built for war, not for ferrying tourists. The tours here are complete with exuberant drivers who play loud music and quack through speakers.
"These are military craft that were never designed to navigate narrow city streets," said Steve Bulzomi, the attorney for a motorcyclist who was run over and dragged by a duck boat that came up behind him at a stoplight in Seattle in 2011.
"This is a business model that requires the driver to be a driver, tour guide and entertainer at the same time," Bulzomi said.
About 45 students and staff members from North Seattle College were traveling Thursday to the city's iconic Pike Place Market and Safeco Field for orientation events when witnesses said the duck boat suddenly swerved into their bus.
Brad Volm of Philadelphia was driving in another vehicle and said the amphibious vehicle's left front tire appeared to lock up.
Authorities say it's too soon to determine what caused the crash that killed the students, from Austria, China, Indonesia and Japan.
The president of Ride the Ducks Seattle said his main concern was for the families of the victims. Brian Tracey said that "we will get to the bottom" of the crash.
Tracey said 36 people were on the vehicle, whose driver had Coast Guard certification and a commercial driving license. All company drivers are required to take continuing education classes, he said.
"We take these issues very seriously," Tracey said.
Seattle Mayor Ed Murray said Ride the Ducks Seattle has voluntarily sidelined its vehicles for the time being.
He wasn't sure whether the duck boats would be allowed to continue in the city. But he said the National Transportation Safety Board was interested in duck boat safety because such vehicles are operating in other cities.
"We'll study this incident in-depth," NTSB spokesman Eric Weiss said. "Of course we look at things that will be of national significance, but we are investigating this accident."
The safety of the amphibious boats has been questioned before. They are remnants from when the U.S. Army deployed thousands of amphibious landing craft during World War II. Once the war was over, some were converted to sightseeing vehicles in U.S. cities.
Thirteen people died in 1999 when an amphibious boat sank to the bottom of Lake Hamilton in Arkansas in an accident the NTSB blamed on inadequate maintenance.
In 2010, a tugboat-guided barge plowed into a duck boat packed with tourists that had stalled in the Delaware River near Philadelphia. The crash sank the duck boat, and two Hungarian students died.
The tug operator was sentenced to a year in prison after acknowledging that the accident was largely a consequence of his use of a cellphone and laptop computer while he was steering the barge.
In July, the family of a woman struck and killed by an amphibious tourist boat in Philadelphia filed a wrongful-death lawsuit.