Szenja (SIN'-jah) was a 21-year-old female. The park says she died Tuesday.
A necropsy is planned, but the park says it could be several weeks before the cause of her death is known.
Szenja was born at a zoo in Germany in 1995. Two years later, she was brought to SeaWorld when the park opened its Wild Arctic exhibit.
The oldest polar bear in the United States, a female called Uulu (OOH'-loo), died last Friday at the San Francisco Zoo. She was 36.