Tashan Weir also called Tuoshan Weir or Tuoshanyan is an ancient dam that was erected under Emperor Tang Wenzong during the Tang Dynasty in 833. The dam is located in Tashanyan Village, Yinjiang Town, Haishu District, Ningbo, Zhejiang, China. Originally designed under the supervision of Wang Yuanwei, who was the administrator of Yin County, in an attempt to prevent tidal sea water from accessing the banks of the Fenghua River and to store water during periods of severe drought. The dam later became part of a large-scale irrigation system serving Ningbo City. This infrastructure is particularly notable because it is recognized as a historical site protected by the state.