Holocene fluvial and marine deposits have accumulated in a graben-like structure on the northeastern margin of the Nile delta. This part of the delta, which includes Lake Manzala, Port Said, and the northern Suez Canal, has subsided rapidly at rates of up to 0.5 centimeter per year since about 7500 years ago. This subsidence has diverted at last four major distributaries of the Nile River into this region. The combined effects of continued subsidence and sea level rise may flood a large part of the northern delta plain by as much as 1 meter by the year 2100. The impact of continued subsidence, now occurring when sediment input along the coast has been sharply reduced because of the Aswan High Dam, is likely to be substantial, particularly in the Port Said area and as far inland as south of Lake Manzala.