The purest, the deepest, the most beautiful lake in the world – Lake Baikal. It is inherent, it is the starting point, without which there is no concept of a homeland for Russian people. But today Baikal is in trouble. On its shores spirogyra, a water-plant, runs riot. It pollutes the coast, displaces rare species of plants and animals. There are rotting piles of this plant on the shores. The crew of the film went on an expedition with scientists of the Limnological Institute to find out what is the cause of the tragedy.
