While building Mae Wong Dam to defend flood in Nakhon Sawan, my classmate thought which side was right and looked in the detail of each opinion. First side that protested to build the dam consist of environmentalists, university students and other people that supported this opinion which led by Mr. Sasin Chalermlarp, secretary-general of the Seub Nakhasathien Foundation, their proposal were on ecology and economic effect topic. While and after building, the ecology effect was formed to deforestation and endanger animals and economic effect was the effective on using money and increasing in public debt. There was a better method if the government used money on others infrastructure like weir or reservoir (in the order to defend flood), and the public debt affected several aspect in economy system like increasing of living cost or higher tax. Another side which supported to build the dam was the people who live in area; their requirement was about their living, the support of water resource on their agriculture and the job that came with the dam project.