the rapid development of intensive farming and enterprises has also led to the increasing severity of non-point source pollution. Over the past 30 years, the primary source of water pollution has changed from point source pollution to a combination of point and non-point source pollution. Figure 2 gives the distribution of total phosphorus in china. it demonstrates that most lakes with phosphorus concentration over 0.025 mg/l are distributed in the eastern area. this phrnomenon is a result of urban rxpansion due to rapid economic development.