This French documentary examines the environmental impact of large substitution reservoirs, often called megabassins, on river health and biodiversity. Set in the Marais Poitevin region, the film follows the efforts of various individuals, including a farmer, a hydrologist, and local activists. Through the experiences of people such as Anne-Morwenn, David, Patrick, and Yann, the story explores the struggle for equitable water distribution and the push to transform current agricultural practices.

The film was directed by Sophie Averty and produced by Emmanuelle Jacq. Its production was supported by several organizations, including France Télévisions, CNC, PROCIREP, and the Région des Pays-de-la-Loire. Released on December 10, 2025, the project focuses on the tension between industrial water storage and ecological preservation.