Difficulties in the treatment of black and odorous rivers: pollution source control: nitrogen and phosphorus nutrients in water bodies seriously exceed the standard. The water system completely destroys the self-purification ability of water body, and the characteristics of black and smelly rivers are poor. The bottom of the river hardens, and so on. The key point of the treatment of black and odorous rivers is to build a water system and restore the self-purification ability of water bodies. It is important to control the entry of pollution sources, especially the direct discharge of sewage.