The oceans cover 70 % of the planet’s surface and regulate the climate. They are the largest reservoir of life on Earth. Yet, over‑fishing, plastic‑induced pollution and coral bleaching are harming them. Hugo Clément travels to Mexico to meet Benjamin, a young Frenchman risking his life to save the last remaining vaquitas, a dolphin species on the brink of extinction. In southern France, world‑champion freediver Guillaume Néry raises the alarm about Mediterranean degradation. Finally, in Australia, Rémi joins activists opposing the mining industry threatening the coral reef.