Tonghui River,Liangshui River, Qinghe River, Bahe River, flows through it and more than 30 large branch riversinterflow with the total drainage area of 1,255km2. The current water system of the city zone is composedof the southern and north water half-loops, which connect with 26 lakes. Many rivers and lakes wereexcavated manually in different historical stages. Moreover, the diversion canals of the Yongding Riverand the Miyun Reservoir were built after the founding of the People's Republic of China.Presently, the existing river and lake water system of the city zone is confronted with many problems, forexample, the insufficient flood-carrying capacity, the hidden danger of flood; the obviously increased rateof surface runoff with the progress of urbanization; the lack of water source;the high degree of pollution,the increasingly deteriorating riverside environment; the disordered construction during the "CulturalRevolution" period did great damage to the water system and it has not yet recovered from it.Beijing is the capital of China and national political, economic, cultural center, and also a centuries-oldcivilized ancient capital. The upcoming Beijing 2008 Olympic Game makes it advance toward aninternational metropolitan and its special position and development prospect bring up higher requirementof the environment. In the light of the present situation and the future development requirement, thecomprehensive treatment of the city water system is put on the top of our agenda.In 1997, with the support of Beijing Municipal People's Government, China Academy of Urban Planningand Design prepared the "Plan for Comprehensive Control of Beijing City-Zone River and Lake WaterSystem", in which the work task between 1998 and 2010 was put forward. The objective of waterenvironmental control is: to turn the water system within the first and second ring road into garden landscape watercourse, and make the water clean and flow merrily; to enhance the flood control capability of the city zone and practically implement the projects of the "water conservation of the west, water drainage of the east, flood diversion of the south and north"; to develop the sewage intercepting project of the water system within the limit of the first and second ring road and make the quality of water meet standard　（GHZB 1-1999）. "Two rings", i.e. south waterlocked system and north waterlocked system, are the two water systems passing through the city zone. The southern one is composed of the Kunming Lake, the Kunyu section of the diversion canal of Miyun Reservoir, Yuyuan Pon, Bayi Lake, the lower reaches of the diversion canal of ~ongding River, the south city moat and the upper reaches of Tonghui River, etc.; the northern one is composed of the Changhe River, the North Moat, Liangma River, Shuidui Lake （in Chaoyang Park）, Honglingjin Lake （in Honglingjin Park） and Erdao Gou.