"The two phases of the lake and the autumn moon are harmonious, and the surface of the lake has no wind mirror." The lake is a regulator of water resources. When it is dry, it is a large reservoir that sends charcoal in the snow. When it is flooded, it is a flood storage pool. It provides products for human beings and is also a beautiful urban landscape. More importantly, it is also an indispensable member of the life community of mountains, rivers, forests, fields and lakes. This episode leads the audience to wander among the lakes and mountains, and understand the importance of lakes in the ecosystem.