Hapi (sometimes Hapy, to distinguish him from the unrelated god Hapi the son of Horus, who was a different deity) was the personification of the annual Nile inundation — the flood that each summer rose from the cataracts, swept down the country, deposited its rich black silt upon the fields, and made Egyptian agriculture possible. He was depicted in a curious form, not common elsewhere in Egyptian iconography: a man with pendulous breasts, signifying nourishment; a thick belly, signifying abundance; blue or green skin, signifying the river's waters; and a crown of papyrus or lotus, signifying the plants of the Nile's two regions, Upper and Lower Egypt. Two Hapi figures (one for each region, the one with papyrus, the other with lotus) were often shown together, tying the plants of the two halves of Egypt around the symbol of unification — a standard motif of pharaonic iconography asserting the Egyptian state's unity from the cataract to the Delta.

Hapi had no great temple — for the inundation came everywhere, and was not localized — but small shrines at Gebel el-Silsila and elsewhere preserved his cult, and at the moment of the inundation's arrival each year, offerings were thrown into the river to thank him for his bounty. The Hymn to Hapi, preserved in a Middle Kingdom papyrus, is among the most rapturous of Egyptian devotional poems. "Praise to thee, Hapi, who comest forth from the earth, who comest to nourish Egypt.... Thou makest the granaries to overflow.... When thou art high, the land is in joy.... When thou retreatest, every face is dark."