One of the most harrowing film sequences you are likely to see this year is in “Blackfish,” Gabriela Cowperthwaite’s gripping documentary on SeaWorld’s captivity of orca whales, and the lethal consequences that have arisen from keeping this awesome species in cement pools for the enjoyment of water park visitors. (The film airs on CNN October 24.)

In the sequence, we watch 2006 footage from a SeaWorld Shamu show gone stomach-turningly wrong. Near the end of a “performance,” an 8,000-pound killer whale drags its trainer to the depths of a tank and holds him there for approximately a minute. The whale then brings the man back to the surface and, moments later, drags him down again. The horror continues this way for minutes -- which feel like years.

The trainer in question, Ken Peters, we learn is both an experienced orca trainer and deep-sea diver, a background that ultimately saves his life as he refuses to panic, but instead pets the whale as it holds his foot in a vice-like bite. He practices ventilation techniques during the few seconds he’s brought to the surface, and eventually is released and able to swim to safety. Thankfully, director Cowperthwaite edits this footage, and we aren’t forced to watch it uncut.

Other trainers from SeaWorld haven’t been as lucky as Peters. The focus of the film stems from the much-publicized death in 2010 of Dawn Brancheau, a young woman who was drowned and mangled by a whale named Tilikum. Incredibly, this wasn’t the first time Tilikum had attacked and killed a water park employee. So how did this massive animal end up in yet another amusement venue, as the star of a show where he was in constant physical contact with his human trainers?

Cowperthwaite isn’t out to make “Jaws.” (She does include a couple of clips from 1977's “Orca,” however.) There is no animal demonizing here. Instead, SeaWorld is in the hot seat. Beginning with the history of orca captivity in the 1970s, “Blackfish” traces how a species which, in the wild, has shown zero hostility toward humans, could evolve into such a dangerous and unreliable predator in close quarters.