Lolita, an orca whale who had lived in captivity at the Miami Seaquarium since 1970, died Friday afternoon, according to the facility.

Lolita began exhibiting "serious signs of discomfort" over the past several days, according to an Instagram post from the Miami Seaquarium. After being treated "immediately and aggressively" by a medical team, she died from "what is believed to be a renal condition" on Friday afternoon, the aquarium said.

"Toki was an inspiration to all who had the fortune to hear her story and especially to the Lummi nation that considered her family," the post reads. "Those of us who have had the honor and privilege to spend time with her will forever remember her beautiful spirit." The Lummi Nation is a Native American tribe based on the coast of Washington state and southern British Columbia, near the waters where Lolita was captured.

The 57-year-old whale, sometimes called Toki and known as Sk'aliCh'elh-tenaut by the Lummi people, was set to be released back into the ocean, the Miami Seaquarium announced in March. Advocates identified a natural sea pen off Washington state, including waters where members of Lolita's family still swim. Her 95-year-old mother is believed to still be alive.

Miami-Dade County Mayor Daniella Levine Cava said in a statement that locals were "profoundly saddened" to hear of Lolita's passing.

"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," 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," the mayor went on.

Eduardo Albor, the CEO of The Dolphin Company, which operates the Miami Seaquarium, also voiced his sorrow over Lolita's death.

"Not a single effort we made to give Lolita an opportunity was a waste of time & money. My heart is truly broken," Albor said in a social media post.

Animal welfare activists, Lummi elders, and the non-profit Friends of Toki advocated for the whale's release as scrutiny has fallen on the practice of keeping whales in captivity. Sacred Sea, a Lummi advocacy group, said the whale "is family to us, and as such, we must care for her as we do our own," in a statement calling for her release. "Together we can right the wrong of Sk'aliCh'elh-tenaut's capture, and safely and responsibly bring her home to the Salish Sea."

Lolita was one of the two oldest orcas in captivity and the only orca caught in US waters still in captivity, according to Friends of Toki. She was captured off the Pacific Northwest in 1970. The whale stopped performing for the public in 2022 and lived in an 80 feet by 35 feet tank, according to CNN's previous reporting.

Friends of Toki had advocated for her release and was working with the aquarium to prepare the whale for her eventual cross-country flight and relocation back to the ocean. Veterinary specialists with the non-profit regularly assessed Lolita's health. Their last report, from July 31, said that Lolita was in "relatively stable" condition with steady energy and appetite -- but was experiencing a bout of abdominal discomfort. On August 15, the aquarium said she was "very stable" and "as good as she can be at 50 years of age."

Medical teams from the Miami Seaquarium and Friends of Toki treated her before she died, both organizations said.

CNN has reached out to Friends of Toki for a statement.