The film is now in post-production, and Lumina is helping with finishing funds. A Sundance launch is possible.
Big River Man follows eccentric Slovenian endurance swimmer Martin Strel as he attempts to swim the Amazon.
'It's a film with a strong environmental message, but it's framed in this fantastic character of Martin Strel,' said Lumina's Samantha Horley.
Revolver Entertainment already has UK rights.
Producers are Molly Lynch (Starship Troopers, Armageddon), who also worked on Maringouin's last film Running Stumbled, and Maria Floria, who has worked on Oscar-winning Broken Rainbow and Tibet: Cry Of The Snow Lion, and Molly Hassell. Mickey Cottrell, Olivia Newton-John, and Kevin Ragsdale are executive producers.
The film-makers said the project is 'not a sports documentary, but a character piece, a tragi-comic journey towards greatness.'
Lumina picked up the project after viewing footage in Toronto.