The Dianshan Lake, which is an important water resource located in the upstream of the Huangpu River, is the only natural lake in the Shanghai region and therefore the major water body monitored over the years. Its water quality directly affects the quality of the drinking water in Shanghai.
According to data from the 13 monitoring sites in the Dianshan Lake, the pH, dissolved oxygen, CODCr, BOD5, volatile phenol, total oxide, total Hg, total Cd, nitrogen nitrate, nitrogen nitrite and chloride are all able to meet the limit of category 1 standard in Environmental Quality Standard for Surface Water (GB3838-88). For instance, whereas the average concentration of dissolved oxygen was 9.26 mg/L, the concentration of Total P and N, which were the main variables affecting the water quality, were 0.11 mg/L and 2.85 mg/L respectively and would, thus, only meet category 3 or category 4 standard. This monitoring result indicated that eutrophication was the main cause of water pollution. In addition, petroleum pollution was relatively heavier and could only meet the category 4 standard. pH in the Dianshan Lake was also higher than the other water bodies in Shanghai because of the relatively higher concentration of unionized ammonia that only met the limit of category 4 standard for water quality.
Compared with the monitored data in the 1980s (figure 15), the organic pollutant and degree of eutrophication had increased sharply. The concentration of petroleum has been controlled and the level of heavy metal pollution had slightly increased but was still within the limit of category 2 standard for water quality. The water quality of the Dianshan Lake is generally good.