The layout of sampling sections should comply with the following principles:
(1) Fully consider the number and distribution of water intake and discharge (return water) outlets in this river section (area), the status of pollutant discharge, hydrology and river topography, the situation of tributary inflow and water projects, the vegetation and soil erosion situation, and other factors that affect water quality and its uniformity.
(2) Strive to obtain the most representative samples with a relatively small number of monitoring sections and measurement points, and comprehensively, truly and objectively reflect the water environmental quality of this area and the temporal and spatial distribution and characteristics of pollutants.
(3) Avoid dead water and backwater areas, and select sections that are straight, with stable riverbanks, smooth water flow, without rapid currents and rapids, and where transportation is convenient.
(4) Try to combine with hydrological sections to obtain relevant hydrological data.
(5) After the section location is determined, fixed signs should be set up and it should not be changed arbitrarily; if changes are necessary, they should be approved by the original approving unit.