The body of Phil Chiang of Palo Alto, California, was taken to the Utah state medical examiner's office for an autopsy.
Chiang's family rented a ski boat and stopped in a cove near Warm Creek Bay, the National Park Service said. Two children went swimming without life jackets and the 49-year-old father jumped in to save one of them when the child began to struggle.
He was able to get the children back on the boat but then went underwater himself. Three nearby boats quickly helped search for him, finding him 10 minutes later.
Lake Powell, which sits on the Utah-Arizona border, is the second-largest reservoir in the United States. It's located in the Glen Canyon national recreation area, which encompasses more than 1.25 million acres.
It's at least the second drowning to take place at the popular tourist destination this year. Subrahmaniyan Mathimohan, a 34-year-old man from Phoenix, drowned after sliding off a rental house's slide in May without a life jacket.
The Associated Press contributed to this report.