The ancient Egyptian god of the Nile inundation and fertility is Hapi (often spelled Hapy in older literature, but Hapi is the standard Egyptological transliteration). There is no distinct god named "Hapy."
Depicted as an androgynous, rotund figure with pendulous breasts and a ceremonial false beard, wearing a headdress of papyrus (North) or lotus (South). Blue or green skin symbolizes water and vegetation. Often shown tying the sema-tawy (unification of Upper and Lower Egypt) or offering overflowing vases.
Hapi was not a state god with major temples but a personification of the annual flood. The "Arrival of Hapi" was celebrated at the start of Akhet (inundation season). Offerings were made at the riverbank; no dedicated priesthood is known. His "cult center" was the First Cataract (Elephantine/Aswan), where the flood was first measured.
Do not confuse with Hapy (Hapi), one of the Four Sons of Horus (baboon-headed protector of lungs). Different deity, same name root.