A two-year-old sea lion, named Sophie, was found dead Friday morning at the bottom of her pool at the Smithsonian’s National Zoo.

Officials put out a tweet saying they were “sad to announce that our beloved sea lion” was dead. Keepers said her behavior was normal when she was checked on Thursday evening.

Officials at the zoo said they “don’t yet know what caused [Sophie’s] death, but they expect to perform a necropsy Friday and have results in the coming weeks.

Sophie is the daughter of Calli. She was born two years ago when the National Zoo sea lions were living at the Pittsburgh Zoo while their new home in the American Trail exhibit in Washington was under construction.

Sophie’s survivors include her mother and two other sea lions, named Summer and Sidney, whom she is not related to.

Sophie (Courtesy of Smithsonian National Zoo)

Sea lions typically have a life span of 15 years to 20 years in the wild and 25 years to 30 years when in human care, according to zoo officials.

Sophie’s death comes on the heels of another National Zoo animal’s passing. Koa, a 6-year-old male brown kiwi bird, was found dead in late April. Initial reports indicated Koa had heart disease, the zoo said. Kiwis are a flightless bird.