Sampling sections should be set up at both ends of the survey area, and sampling sections should be set up in the water areas near key protected objects within the survey area. Sampling sections should be set up near sudden changes in hydrological characteristics (such as tributary confluence), sudden changes in water quality (such as sewage discharge), key hydraulic structures (such as water intake, bridges and culverts), hydrological stations, etc., and other locations that require water quality prediction should be appropriately considered.