What do you do for an encore when you have already swum the Mis sissippi, Danube and Yangtze rivers?

If you’re Slovenian daredevil Martin Strel, you try to swim the mighty Amazon, all 3,000-plus miles of it.

Strel’s 2007 adventures on and in the Amazon are detailed in John Maringouin’s fun documentary “Big River Man.”

Strel doesn’t seem to be fit for endurance swimming — he’s fat, has high blood pressure and eats (horse burgers) and drinks (two bottles of red wine a day) too much.

But those shortcomings can’t deter the 55-year-old, whose team includes his son Borut, who also serves as the film’s narrator and his dad’s media spokesman.

The quest takes its toll — physically and mentally — as Strel is afflicted with blisters, sunburn and exotic stomach illnesses.

As the mood darkens, you can’t help but be reminded of Klaus Kinski’s twisted character in Werner Herzog’s 1972 “Aguirre: The Wrath of God.”