Watch "Blackfish" Sunday night on CNN at 9 and 11 ET.
(CNN) -- Nearly 21 million people watched "Blackfish" when it aired on CNN in October.
The documentary, produced by Magnolia Pictures and acquired by CNN Films, recounts the 2010 death of veteran SeaWorld trainer Dawn Brancheau by a killer whale named Tilikum, a 12,000-pound bull.
The film challenges the concept of keeping killer whales for entertainment and implies Tilikum had been driven to madness by captivity.
In the months since, a firestorm of debate over the controversy erupted.
Social media exploded with an outcry to boycott SeaWorld, the world's largest marine park operator.
Protesters not only lined the streets outside SeaWorld Orlando in Florida, the company's flagship park, but the streets of New York and Pasadena during the Macy's Thanksgiving Day Parade and the Rose Parade.
Southwest Airlines, which owns a plane with a killer whale painted on it, also received a taste of the "Blackfish" backlash. A handful of protesters presented a petition to an airline spokeswoman asking it to end its business relationship with SeaWorld. Southwest responded in a statement it was not contemplating changes to its multi-year contract with the entertainment company.
Perhaps the largest fallout was in the form of a virtual cavalcade of musicians backing out of SeaWorld's "Bands, Brew & BBQ" concert series.
Willie Nelson, Trace Adkins, Trisha Yearwood and Joan Jett are among those who declined to perform at the theme park over the controversy.
SeaWorld has battled back against the claims "Blackfish" makes, calling the film grossly one-sided and the product of animal activists.
The company has declined CNN's repeated requests for interviews, but has responded to written inquiries.
"Blackfish is billed as a documentary, but instead of a fair and balanced treatment of a complex subject, the film is inaccurate and misleading and, regrettably, exploits a tragedy that remains a source of deep pain for Dawn Brancheau's family, friends and colleagues," SeaWorld said in a statement.
"To promote its bias that killer whales should not be maintained in a zoological setting, the film paints a distorted picture that withholds from viewers key facts about SeaWorld -- among them, that SeaWorld is one of the world's most respected zoological institutions, that SeaWorld rescues, rehabilitates and returns to the wild hundreds of wild animals every year, and that SeaWorld commits millions of dollars annually to conservation and scientific research."
In January, Brancheau's family distanced themselves from the documentary.
"Blackfish is not Dawn's story. Dawn Brancheau believed in the ethical treatment of animals. Dawn followed her dreams and became a marine animal trainer. She loved the whales and was proud of her work as a trainer," a statement on a charity website dedicated to the slain trainer said.
"Dawn would not have remained a trainer at SeaWorld for 15 years if she felt that the whales were not well cared for. Trainer safety was important to Dawn, and it remains important to us as well. Our family always supported Dawn and we continue to support Dawn's friends and co-workers who currently care for the animals she so loved."
Former killer whale trainer Mark Simmons appeared in "Blackfish," but after its airings has gone on to become one of the film's most outspoken critics.
"SeaWorld has exemplified the best in care of their animals and personnel for nearly six decades," Simmons said. "The Blackfish crusade against SeaWorld and zoological care in general is engineered by a perfect marriage between sensational animal rights organizations and disgruntled ex-SeaWorld employees."
Meantime, the marine park giant announced record fourth-quarter results and record annual revenue results in January, indicating there appears to be no real impact on its business.
But some animal activists say behind the scenes, SeaWorld is worried.
The company launched expensive full-page ads in America's top newspapers and local publications where its parks are located.
A promoted link at the top of a Google search takes Internet users to a section within SeaWorld's website called, "The truth about Blackfish."
Others have even suggested recent financial moves hint of trouble.
In December, SeaWorld's largest investor, the Blackstone Group, sold its majority ownership the month before SeaWorld's own chairman sold more than a million dollars' worth of his SeaWorld stock.
Financial analysts cautioned that both cases may be routine investment transactions and not an indicator of any concerns.
Last weekend, SeaWorld kicked off its concert series with Kid Rock and Alan Jackson, and despite the protests outside — inside, the crowd was robust. The next scheduled acts, Gretchen Wilson and Bill Engvall, are also expected to perform before an at-capacity crowd, the company said.
The show, much like the debate Blackfish continues to spark, goes on.