A powerful documentary. You'll think twice about planning on a trip to Seaworld, swimming with the dolphins or watching reruns of Flipper after this.

"I'm not exaggerating - if they could kill me, they would," says Ric O'Barry, a former dolphin trainer turned activist. O'Barry was one of the worlds first dolphin trainers; he captured and trained the five dolphins that starred in the '60s Australian TV show Flipper, but has since dedicated his life to freeing dolphins wherever and whenever he can. His actions have got him into numerous scrapes with the authorities: when asked how many times has he been arrested, O'Barry replies "This year?" O'Barry's path to redemption has taken him to the island of Taiji, Japan, where 23,000 dolphins are killed every year. Some of those captured are selected by various water parks around the world and shipped off (sometimes at $150,000 a dolphin); those rejected are slaughtered in the titular cove hidden from public view, the massacre literally turning the sea red. With the help of various activists - and some nifty camouflaged cameras courtesy of Industrial Light & Magic - O'Barry assembles a team to capture the killing on camera for the first time... But these people have powerful friends.

O'Barry is as determined as he is honest: he blames Flipper - and himself - for creating the "dolphin culture" that has swept the world since the show's airing. O'Barry is not only up against public ignorance. This has been kept a secret until now - he's up against the Japanese government (who have him tailed every time he's in the country), the aggressive security in Taiji, and the ineffectual International Whaling Commission (described here as "toothless"). To encourage the sale of dolphin and whale meat, the mayor of Taiji introduced a free lunch system in schools. Not only is that disgusting, but both cetaceans have a high level of mercury, the most toxic, non-radioactive, substance in the world. Japan has a history of this: in the '50s the sale of whale meat led to widespread physical and mental handicapped births.

Debutant director Psihoyos unloads this awful information on increasingly appalled viewer with a 'if you thought that was unforgivable, wait until you hear this...' manner. Although The Cove does attempt to cover the fishermen's side of the story, a side hampered by their lack of communication that's limited to 'dolphin fishing is our history', the documentary can be accused of being one-sided. But there's only one side you can take.