Marshization of water bodies is a serious problem of the global water environment.Water marshization mainly occurs in lakes.It also happens to slow-moving or standing rivers.Geographically, lakes have a natural tendency of marshization. Over time, lakes become filled with sand, mud and sediment of chemical and biological substances. Water gets shallower until finally lakes turn into marshes or even disappear completely. Human activities have great impacts on the process of marshization. They can either accelerate the course or slow it down. Based upon a description of this notion, the thesis explains the relationship between tourism development and environmental protection.The author indicates that only protection-oriented development is positive. The West Lake in Hangzhou is a good case in point. The lake was a lagoon that was formed from the bay at the mouth of the Qiantang River as the sand and mud from both the river and sea piled up until finally the bay got separated from the open sea. The process of marshization began when the standing salt water turned into a fresh water lake around 2000 years ago. If left to the natural process, the West Lake would have disappeared long ago for sediment. It exists today because human activities effectively hindered its marshization course. For over one thousand years, man launched more than a hundred dredging campaigns that successfully prevented it from becoming land. It is man's constant fight over long time that has contributed to the beautiful scenic area of today's West Lake. With an analysis of the development activities to the lake in the past 20 years, the thesis concludes that both positive and negative development continues to occur. This is a common phenomenon in the development of many similar lakes in China.The thesis argues that human practices of both ancient and contemporary times have proved sustainable development is the only desirable way for human being.