“Blackfish” suggests that audiences at water parks have witnessed near misses that could have ended badly for orca trainers.

“I don’t come from any animal activism,” Cowperthwaite says. “I’m a documentary filmmaker, but I’m also a mother who took her kids to SeaWorld. So I actually thought I was making a completely different movie, a grand movie about human beings and our relationship with our animal counterparts. Making this film was my education.”

“Blackfish,” which opens Friday, is ostensibly about Tilikum, a SeaWorld orca connected to the deaths of three people (including, most recently and famously — thanks to YouTube footage — that of Dawn Brancheau at SeaWorld in Orlando in 2010). The film, however, is actually a searing indictment of the training techniques used by SeaWorld and other aquatic parks, and of the practice of keeping wild animals, particularly predators, in captivity.

Cowperthwaite presents interviews with animal experts and trainers — including some who have had contact with Tilikum, who still performs at SeaWorld in Orlando — and intersperses them with cellphone and video footage of aquatic near misses that occurred in front of hundreds of children clutching Shamu stuffed animals. Most of the people capturing the footage had no idea they nearly recorded someone’s death, Cowperthwaite says, and she herself didn’t realize how keeping an orca in these restrictive environments could turn the animal from dangerous to malicious.

“There came a point when I was learning things just as I was filming them, so it was almost the purest form of documentary filmmaking,” she says. “There was no script. I had to be comfortable with the future being a question; I had to be open to the truths that were laid out before me.”

Throughout the process, Cowperthwaite says she continually thought, “I can’t believe I’m making this documentary that’s exposing this depravity,” she says. “And I can’t believe I’m the same person who enjoyed myself and brought my kids to these parks.”