(Arabic: عيد وفاء النيل‎) has been an important natal cycle in Egypt since ancient times. It is celebrated by Egyptians as an annual holiday for two weeks starting August 15, known as Wafaa El-Nil. It is also celebrated in the Coptic Church by ceremonially throwing a martyr's relic into the river, hence the name, Esba` al-shahīd ('The Martyr's Finger'). Ancient Egyptians believed that the Nile flooded every year because of Isis's tears of sorrow for her dead husband, Osiris.

The three stages of the Egyptian flood cycle were Akhet, the time of the Nile flood, Peret, the sowing time, and Shemu, the time of harvest. Without this cycle people would die from starvation.The flood cycle was so predictable that the Egyptians even based their ancient calendar on it. Akhet was the first season of the year, between the months of June and September. Peret or the Egyptian Autumn season marked the time when their crops grew in the fields and were harvested,^[1] running from October to mid-February. Shemu was the third and last season of the Egyptian year which ran from mid-February until the end of May; it essentially signalled the spring season of the Egyptian calendar.^[2]