The annual flood of the Nile River that occurred in ancient times was caused by rains in Central Africa and melting snow and rains in the Ethiopian highlands. In May, just prior to the flood, the Nile was at its lowest point. From June to August, the river rose rapidly, carrying a brown silt in its waters. The flood was at its highest point in mid-September; it took eight to ten days for the crest to pass downstream from Elephantine to Memphis. By October the waters began to recede, leaving pools of water in depressed areas of the floodplain. After the water was absorbed by the soil, the ancient Egyptians planted their crops in the mud.

The ancient Egyptians used a device called a nilometer to record the level of the river during the inundation. Nilometers were staircases that descended into the Nile with marks indicating various levels above low water.

The annual inundation continued into modern times. With the completion in 1988 of the high dam at Aswan (ancient Elephantine), however, the flooding has been controlled.