The waterway transport from Day mouth to the Ninh Phuc (Ninh Binh) port is strategic waterway of the North. The effect of waterway transport is great and convenient for transporting goods from the South, the central provinces, without transit through the Hai Phong port. However, the alteration of fairway on the layout following season, year is the biggest obstacle for exploiting this fairway. Based on analysis of available data on natural conditions, the article focuses clearly the progressing rule of Day mouth and directing solutirns of regulating Day mouth for serving navigation.