In February 2010, reports of the accidental death of a killer whale trainer, Dawn Brancheau, at SeaWorld, Orlando featured in newspapers and TV bulletins across the globe. How could such a tragedy occur? What on earth was Brancheau thinking? How could she make such a silly mistake? Then the story changed and it appeared this very experienced trainer was attacked by the orca, Tilikum. Shockwaves rippled. What? A gentle giant killed a human that cared for it? Suddenly killer whales lived up to their fearsome moniker and became the villains of the moment.

Then the story changed again and the truth began to emerge…

Blackfish is a startling documentary from Gabriela Cowperthwaite that investigates the reality behind the sparkling waters and bright lights of the SeaWorld parks, not that they are alone in their mistreatment of these startling, intelligent, beautiful creatures. She trawls through the archives to reveal that Brancheau's death was neither a freak accident nor an isolated attack from a vicious animal, but just one of many examples since humans decided it was acceptable to kidnap young orcas for the pleasure and pockets of humans. Kidnap? Is such a strong word appropriate? Watch Blackfish, listen to the mother make "sounds we've never heard an orca make before" in a harrowing display of grief and then decide.

Watching Blackfish and still choosing to visit SeaWorld or another such aquatic zoo is surely on the same level as taking your kids to McDonalds even though you know you're poisoning them. If I were reviewing the subject of Blackfish, like 2009's powerfully distressing The Cove, it would surely warrant a perfect score. Upon the evidence here, even if you've chosen not to see the truth of our actions in the past, there's no contest. It's wrong, it's unacceptable, it's a despicable thing we do when we steal these creatures from their oceans and trap them in tiny prisons. But the review is not for the subject matter but for the manner in which it is presented to us.

Blackfish isn't perfect. It doesn't have quite the same profound, lasting impact as The Cove. Perhaps that is, in part, down to the lack of shocking imagery. The footage of orcas bleeding copiously into their pools, having been attacked by other killer whales, is sickening but because it is on a smaller scale than the mass slaughter of dolphins that dyed the cove scarlet there is a risk the impact will be reduced. It shouldn't be, it mustn't be, but… We shouldn't need to see it to believe it, but we've become a far more visually inspired breed in recent years.

More than that, Blackfish doesn't give a lot of time to the other side of the story. I'm intrigued to know quite how SeaWorld could possibly defend its actions but, as they declined to be interviewed, this is a very one-sided documentary. I can't help thinking this imperative cause would be even more compelling if we could hear the excuses.

Another unexplained mystery is how Cowperthwaite obtained the footage she has of SeaWorld. Presumably they didn't give it to her willingly. But these are minor quibbles with a documentary that is as sickening as it is compelling. Interviews with apologetic, horrified former SeaWorld trainers and tear-streaked 'kidnappers' impart the information we need to educate, inform, convince or perhaps even convert us.

First, Cowperthwaite teaches us about the orcas: Their brains are superior to ours in certain aspects; their emotional attachment far exceeds ours, with offspring remaining with their mother long into adulthood; each family group (or pod) has it's own culture and 'language' for communication.

She then counters that with the lies perpetuated by the SeaWorld staff that we choose to believe: Orcas live longer, up to 35 years, in captivity due to the care available – actually, in the wild, it's up to 50 for males and can be closer to a hundred for the females.

Male dorsal fin collapse is normal – absolutely, it's 100% in captivity. However, in their natural environment it occurs approximately 1% of the time.

Killer whales enjoy performing the tricks in tiny pools for us – um…

As more and more evidence of orca psychosis brought on by cruelty and captivity unfolds, Blackfish becomes increasingly difficult to watch. The sight of peeling paint in a tiny, floating warehouse into which the orcas are herded every night is saddening. Hearing that they are punished for not performing perfectly is horrifying. Watching them bleed, observing them rock in grief or cry out to their stolen offspring is heartbreaking.

The message throughout Blackfish is that faceless managers steal killer whales (along with dolphins and countless other creatures) from their natural habitats, subject them to abuse and solitary confinement in woefully cramped enclosures so that we can pay to watch them perform unnatural tricks for our cameras, and so the owners can watch their bank accounts swell. The message is, it isn't about entertainment or protection of a species, it's about money.

But what stamps the reality more indelibly than anything that comes before it, is the comment from one of the former trainers in the final scene. As they sail through the ocean, watching a pod of killer whales free and at peace in their natural environment, he comments, "We saw orcas swimming in straight lines with straight dorsal fins... it was an honour."

For more reviews from The Squiss, subscribe to my blog and like the Facebook page.

This year is already shaping up to be a great one for documentaries and Blackfish is quickly earning the reputation of being the most essential. And it absolutely deserves it. Although its an emotionally charged argument, there's a rational logic behind it. Every time there's found footage of killer whale incidents it's utterly gut-wrenching and you can't help but dread the moments that inevitably shook the world when they could've been prevented. Fortunately, the filmmakers find a different way to present the footage each time and it keeps it from feeling repetitive and builds to feeling more heart breaking at every turn. In its use of talking head interviews with former trainers, it ends up genuinely dramatic without feeling melodramatic as many documentaries can. It oozes with passion for the creatures which helps enforce its argument against their treatment, not just for better protection for trainers, but for corporations like SeaWorld to not turn a blind eye at the clear injustice they've cased. What's the moral cost of the business and entertainment? I certainly won't ever be able to be entertained by animal acts without thinking about Blackfish. Thisis an extremely powerful documentary that's brilliantly structured, tragic and cinematic. More than worth your time.

8/10