In 2006, water quality monitoring of the water environment of the Three Gorges reservoir area included the monitoring of both the water quality of the mainstream and tributaries of the Yangtze River and monitoring of  water blooms in the tributaries. The assessment of water quality was conducted in accordance with the Environment Quality Standards for Surface Water (GB3838-2002). Whereas the assessment of comprehensive nutrient status of waters was carried out according to "Technical Regulations on the Assessment Method and Classification for Eutrophication of Lakes (Reservoirs)" developed by China National Environmental Monitoring Center.

5.1 Monitoring of Water Quality in the Reservoir Area

In 2006, 13 water quality monitoring sections were established in the reservoir area, 6 of which were along the mainstream of the Yangtze River and located at Zhutuo of Chongqing, Tongguanyi, Cuntan, Qingxichang of Fuling, Tuokou of Wanzhou and Guandukou of Badong. The remaining 7 sections were along the primary tributaries of the Yangtze River, they were Beibei and Linjiangmen of Jialing River, Wulong of Wujiang, mouth of Yulin River, mouth of Pengxi River, mouth of Daning River and mouth of Xiangxi River. Water quality assessment included 13 items such as pH, dissolved oxygen, permanganate index, BOD₅, ammonia nitrogen, petroleum, TP, mercury, cadmium, arsenic, copper, lead and hexavalent chromium.

5.1.1 Water Quality of the Mainstream

In 2006, among the 6 sections along the mainstream, the water quality of Tongguanyi, Qingxichang, Tuokou and Guandukou sections was Grade II-III. The annual water quality of Zhutuo section and Cuntan section was Grade IV due to the influence of petroleum. 66.7% of the sections met surface water quality standard. The overall water quality of the mainstream had some decrease compared with that of 2005. Among them, water quality of Zhutuo section and Cuntan section degraded from Grade III to Grade IV. While water quality of Guandukou section went up from Grade III to Grade II. The remaining 3 sections kept their water quality.

Table 5-1　Water quality of the mainstream of the Yangtze River in the Three

Gorges reservoir area in 2006

Water quality of the mainstream was the best during January-March, May and August, falling into Grade III and 100% water sections meeting the standard. In April, water quality was relatively good and met Grade III standard except the Cuntan section (Grade IV due to petroleum pollution), 83.3% of the monitoring sections met water quality standard. During October-December, the water quality was relatively poor. This was illustrated by the fact that the water of 4 sections met Grade IV standard due to the impacts of TP and petroleum pollution except that of Guandukou section and Tuokou section (GradeII and III). In November, 50.0% sections met water quality standard. In October and December, this figure was 33.3%. Water quality was the poorest in June, July and September with most sections meeting Grade V standard in June and September and failed to meet Grade V standard in July with up-to-the-standard rate of 50.0%, 33.3% and 16.7% respectively. TP and lead were major pollutants.