The characters combine literally to mean “Great Yu Manages the Water.” It's the title of a story that every Chinese person knows.
The story of 大禹治水 is a pillar of Chinese civilization, shaping its values for millennia. It's often taught to children alongside other foundational myths like `盘古开天 (Pángǔ kāi tiān)` (Pangu creating the world). Its core significance lies in its stark contrast to Western flood myths, most notably the story of Noah's Ark.
While you won't hear 大禹治水 in everyday casual conversation, its spirit and related idioms are frequently invoked in more formal or inspirational contexts.