This compulsive, Herzogian documentary from American director John Maringouin (director of 2006’s grimly watchable Running Stumbled) plots a course for the heart of darkness in the company of 52-year-old Slovenian endurance swimmer Martin Strel.

Pot-bellied and fond of a drink, he’s nonetheless a national hero – one who attempts to become the first person to swim the length of the Amazon. Strel’s operation seems dangerously amateurish: a creaking Peruvian boat, a greenhorn American navigator, and his own son (the film’s deadpan narrator) serving as manager and publicist.

Then there are the thrilling perils of the 3,000-mile odyssey: crocodiles, river parasites, lethal whirlpools, giant floating tree trunks, heatstroke…

Maringouin artfully meshes music, editing and camerawork to nail the mental deterioration of his taciturn protagonist, who’s dubbed the ‘Fish-Man’ by the awed local tribespeople.

Undoubtedly manip😼ulative, it also unsettles, fascinates and exhilarates.