The victims, identified by North Seattle College President Dr. Warren Brown, are Claudia Derschmidt, 49, of Austria; Privando Putradanto, 18, Indonesia; and Mami Sato, 36, from Japan.
The fourth victim is Runjie Song, 17, according to the King County's Medical Examiner's Office. Brown previously said she was from China.
Brown said the students had come to Seattle to improve their lives by seeking higher education and it's "absolutely devastating" that Thursday's events will keep them from fulfilling that dream.
North Seattle College has more 1,000 international students from more than 50 countries. Passengers on the bus were employees and students in the international program, the school said.
Nearly 50 people were taken to hospitals in the Seattle area, Susan Gregg, a spokesperson for Harborview and University of Washington medical centers said. The injuries have ranged from head trauma, to facial lacerations to broken bones.
Those most seriously injured -- a total of 17 -- were taken to Harborview Medical Center. Three were immediately taken into the operating room for surgery, Gregg said, and others were triaged to intensive care or other floors.
As of Friday morning, Harborview still had one patient in critical condition and one in serious.
"We all came together and did, I think, the best we could in some challenging situations when you have people who don't speak English, you don't have identities," Gregg said.
It is unclear why the duck boat -- a street vehicle that can double as a boat -- hit the bus across the six-lane Aurora bridge, Lt. Sue Stangl with the Seattle Fire Department said.
Officers were able to help preserve evidence that they, working in conjunction with the National Transportation and Safety Board, will use to help sort out the particulars of the accident.
The bridge, which connects downtown Seattle and the Fremont neighborhood, has since reopened.
Mayor Ed Murray said investigators aren't ruling anything out.
"The NTSB investigation will really help us understand whether it is the structure itself, or the vehicles, or a combination of the two," he said.
The duck boat tour operator issued a statement: "Ride the Ducks of Seattle wishes to express its sincerest condolences to the family and friends of the people who were killed and those that were injured," it said.
Making sure his college's students and faculty receive the emotional, physical and psychological support they need is Brown's top priority.
"I love all graduating classes," he said. "But when this group of international students graduate, I'll be extremely happy for them."
"There's a powerful story they will share," he said.