The Miami Seaquarium has announced that Lolita, a killer whale who was in captivity for at least five decades, has died. Officials were reportedly preparing to send her back to her home waters. Lolita was also known as Tokitae, or Toki. Lolita, believed to be at least 57, was the oldest killer whale being kept in captivity (Miami Seaquarium/Facebook)

In a Facebook post, the Miami Seaquarium said, “Over the last two days, Toki started exhibiting serious signs of discomfort, which her full Miami Seaquarium and Friends of Toki medical team began treating immediately and aggressively. Despite receiving the best possible medical care, she passed away Friday afternoon from what is believed to be a renal condition.”

“Toki was an inspiration to all who had the fortune to hear her story and especially to the Lummi nation that considered her family. Those of us who have had the honor and privilege to spend time with her will forever remember her beautiful spirit,” it added.

"Alongside the many Miamians who grew up visiting her, the generations of activists around the world that were inspired by her story, and the caretakers who remained dedicated to her until the end - today, we say our final goodbye to our beloved Toki," Miami-Dade Mayor Daniella Levine Cava said in a statement. “Our collective wish was to see Toki in her native waters and we are heartbroken to learn of this sudden loss.”

Lolita was caught when she was four years old

Lolita, believed to be at least 57, was the oldest killer whale being kept in captivity. She was caught when she was about four years old, on August 8, 1970, in Penn Cove, Puget Sound in Seattle, Washington, and sold off to the Miami Seaquarium. She arrived and started living with another orca named Hugo. They lived together for about 10 years before Hugo died in 1980.

Animal rights groups have for several years wanted Lolita to be moved to "a protected cove sea pen” and released in the ocean. County officials announced a plan to release her back in March.

"The most important thing is Toki's long-term wellbeing, and together, guided by the experts, we will continue to do what's best for her," Mayor Daniella said at the time, according to CBS News. "This is such a special creature who is loved by so many people around the world. So many are concerned about her well-being after decades of being in a small tank. Here we are looking at the real possibility that she will spend the rest of her life in nature's waters and live freely." The relocation was supposed to occur in the next 18 to 24 months.