When I saw The Cove at this year’s SIFF (it opens at the Egyptian in August), I had no idea what I was really about to see. This heartbreaking documentary is a true eco-thriller, as well as raising important concerns about the current state of our oceans.

The film’s genesis came when Louie Psihoyos, a former National Geographic photographer and executive director of the Oceanic Preservation Society, met Richard O’Barry in 2005. O’Barry captured and trained dolphins for the 1960s TV series Flipper, then recanted and is now a full-time dolphin rights activist.

When they met, O’Barry was about to leave for Taiji, Japan, to protest the annual dolphin slaughter there. Would Psihoyos like to come? Pishoyos was surprised. “I couldn’t imagine that in this day and age that something like that was going on,” he says. Intrigued, he agreed to accompany O’Barry to Japan.

“Dolphin season” in Taiji runs from September to March. “Going into the town, it was so strange,” says Psihoyos. “You really felt like you were walking into a Stephen King novel. There’s this sort of masquerade around town; the mystique around there is that they love and respect the dolphin, but the reality is much different. It’s that dichotomy that drew me—I mean the signs are in English, saying ‘We love dolphins.’”

As the dolphins swim past Taiji, fishermen first herd them into one cove, in public view, where the best are picked for sale to aquariums around the world. The rest are then moved into a hidden cove, off-limits to the public even though it’s in a national park. “They don’t want people going up to the park seeing what’s going on during the harvest season,” Psihoyos explains. “They make up all sorts of excuses. The government says, ‘Oh you’re not supposed to go down the paths because of falling rock. We’re doing it for your safety.’”

O’Barry was well-known to the Japanese authorities, as he’d been photographing the dolphin herding and trying to interest journalists in the story. He certainly came to the attention of the local authorities, resulting in counter-protesters showing up to block him (and others) from taking photos. And when O’Barry arrived with Psihoyos, the two were followed by the police.

“It was scary,” says Psihoyos. “The paranoia was justified, and that’s when I started to realize that there was a bigger story there. You have this police intimidation; they’re following you around, the whalers are following you around, they’re really hiding something. Which begs the question—what are they hiding?”

It’s at this point that The Cove becomes something of an action film, as Psiyohos assembles a team that risk arrest by sneaking into the off-limits areas of the park and planting cameras through various ingenious methods. “Each time that we finished a trip I’d say, ‘That’s it. I can’t go back again,’” says Psiyohos. “Because it just got to be too scary, and too intense. Eventually it was just too hot—as soon as we checked into a hotel there’d be cops outside the door, or cops in the parking lot waiting for us, watching our every move. They had 24-hour police surveillance on us. So we actually launched our last two expeditions from Osaka.”

The cameras captured scenes of the dolphins being slaughtered with stunning brutality. Psihoyos edited 40 hours of footage down to three minutes in what he calls “one of the worst months of my life. It was horrible. I’d literally do it sometimes 12 hours a day. I was in tears. But I was thinking it’s going to be worth it, because there’s going to be hundreds of people looking at this. And it’s going to be important that they see this.”

And that’s just part of the story. The “eco” part of this eco-thriller comes with the realization that the butchered dolphins are sold for their meat—and that it’s so laced with mercury that it’s poisonous.

“It’s across the board toxic,” Psihoyos says. “Every bit of dolphin and porpoise meat that’s been tested in Japan over the last decade has been shown to be toxic by their own government and their own standards. They know it’s toxic and they’re selling it anyway. If you go to the Japanese Ministry of Health, Labor and Welfare website, the first thing they recommend for a pregnant woman, right on top of the list is: bottlenose dolphin. For a pregnant woman—it’s insanity! To recommend toxic dolphin meat as a staple for a pregnant woman is unconscionable.” (The site has since been changed; now only those who aren’t pregnant are assured it’s okay to eat the tainted meat.)

Dolphins aren’t the only toxic animals and fish in the seas of course, thanks to us. It’s a subject Psihoyos feels passionate about and hopes others will as well.

“Audiences have been laughing, you have people crying, you have cheering, and then they’re asking what they can do afterward,” he says. “It’s a dream for a film maker. We’re not just trying to make a movie—we’re trying to start a movement. If I could inform people what’s going on, maybe we could stop this horror show.

“Boy, I’d die a happy man if I could say that I had a hand in saving 23,000 dolphins and porpoises a year.”