Aluminum salt content in the water body and sediment of Hangzhou West Lake was investigated to study the effects of residual aluminum flocculant on aluminum salt content of water, sediment and attachments on submerged macrophyte. The results show that: (1) Aluminum ion content of water inlets is higher than that of the central lake, which caused by residual aluminum flocculants from Diversion Project, while Al₂O₃ content of sediment tend to be distributed evenly across the lake and is not affected by the Diversion Project; (2) With the flow velocity of about 0.04 to 0.20 m/s, submerged macrophyte can easily become attachment receptors to residual aluminum flocculate, but is slightly weaker than sediment in the ability of attaching Al₂O₃ content; (3) Aluminum ion content of water is high in autumn and winter, which may potentially cause greater biological harm to aquatic organism in the lake. Therefore, it is important to restore submerged macrophyte in autumn and winter seasons. Effect of Diversion Project on the West Lake water body is essential but unpredictable. It should be possible to reduce the negative impact of Diversion Project. The use of flocculant can be reduced or environmentally friendly flocculant can be chosen instead, and appropriate aquatic plants may be cultivated near water inlets.