**6.1 Dianchi Lake, China**

Lake Dianchi is the sixth largest freshwater lake in China and a capital city of this province with population of 6 million is located adjacent to the lake (see Fig. 7). The lake is divided into two parts: the northern, smaller part is called Caohai, with a surface area of 7.5km2 and an average depth of 2.5 m; the larger southern and main body of the lake is called Waihai, with a surface area of 292km2 and an average depth of 4.4 m. There are more than 20 major rivers flowing into the lake from the east, south and north. The lake water has been used to support industrial development, urban drinking water, navigation, tourism and irrigation etc.

Due to the rapid growth of population and economic development in the basin (6 million in 2006, only 1.5 million in 1980), this lake has received more and more wastewater that is yielded from the catchment. In 1995, the wastewater was up to 185 million tons, among them, TP (total phosphorous) 1021 tons, TN 8981 tons, more than half of which was nonpoint source pollutants from the agricultural fertilizer or pesticide. The algal blooms have been emerged from the late 1980. The lake has been listed in the ''Three Important Lakes Restoration Act in China'' by the central government. Huge investment has been spent for the remediation, but none of them has been proved effective. The city currently faces a difficult dilemma: whereas on one hand many efforts have been undertaken to improve the local water environment, the pollution problem is still overwhelming. On the other hand, the city is growing and its dependence on the lake, though already severely problematic, is still growing (Huang et al., 2007).

Gray and Li (1999) reported that if Dianchi Lake is to have the high water quality as it had in the 1960s, the TP inflow through surface water should be less than 60 tons per year. Although the government has made many attempts to reduce the TP, Huang et al (2007) drew a pessimistic conclusion: ''The TP load reduction envisaged as realistic would only stabilises the lake water quality by about the year 2008; unfortunately, interventions could not return the lake to its former pristine condition.''

This is understandable as the government does not use the strategy of SPP. Similar to Taihu lake, once the proposed strategy is used, only the clean water is allowed to enter the lake, when the water crisis is curable. The required inner dike is about 163km for the lake to implement the SPP strategy, and the construction of this levee and its associated sluice gates is only a small fraction of the cost required by other alterative.
