CHICAGO (NBC) -- As a pediatric surgeon, saving children's lives was Dr. Donald Liu's job.
The Comer Children's Hospital doctor on Sunday died saving lives outside of the hospital.
Liu, of Chicago's Hyde Park, drowned after successfully saving two children in Lake Michigan, police said.
"The fact that Don would save everything to save a child is what made him who he was. This doesn't surprise any of us," said Liu's colleague, Dr. Jeffrey Matthews.
The 50-year-old surgeon, his wife and three children were vacationing over the weekend in Berrien County Michigan when Liu reportedly saw two children fall out of a kayak.
He was able to get the children to safety before being pulled under by the current himself.
Liu, a surgeon at the University of Chicago Hospital for nearly ten years, led the way in minimally-invasive surgeries for children with cancer, intestinal problems and physical trauma, his colleagues said.
Liu took the most difficult cases, and yet had the time to forge ties between Chicago and Shanghai.
"He was fun to be with, to talk about his heritage, his Chinese heritage. He was fun to talk about politics [and] about baseball," said Liu's close friend, Dr. John Cunningham.
Liu leaves behind his wife, Dr. Dana Suskind, and three children between the ages of 7 and 13.