Excessive water drawn from a large number of dams and reservoirs built on the Huanghe Rivers main course caused cut-off of the water flow in lower course and decreased largely the discharged into the Bohai Sea. There are abundant wetlands and biological resources on the modem Huanghe River mouth delta. Marine biological resources are very rich in the Huanghe River estuary and adjacent sea area, The large decrease in the fluxes of water and sediment imputed into the sea and the cut-off of water flow will change greatly the marine ecological environment. For example, the delta coast will be strongly eroded by wave; the ecological environment of the wetland will degenerate; soil will change due to desertification; diluted water areas will disappear in the estuary; the influence of river water on the temperature of seawater will decrease greatly, nearcoast seawater will be characterized by high salinity, concentration of nutrients, such as phosphate, nitrate, silicate, in seawater will be decreased, etc. The balance of the ecological environment will be destroyed; and the tidal current distribution location of the amphidromic point of the M2 and high speed regions, etc. will change. All these affect greatly the sustainable use of the marine environment and resources in the Huanghe River delta and adjacent sea areas.