Abzu

The Abzu or Apsu (Sumerian: abzu; Akkadian:  apsû), also called engur (Cuneiform:, LAGAB×HAL; Sumerian: engur; Akkadian: engurru—lit.  ab='water' zu='deep', recorded in Greek as  Apasṓn ), is the name for fresh water from underground aquifers which was given a religious fertilising quality in ancient near eastern cosmology, including Sumerian and Akkadian mythology. Lakes, springs, rivers, wells, and other sources of fresh water were thought to draw their water from the abzu. In Mesopotamian mythology, it is referred to as the primeval sea below the void space of the underworld (Kur) and the earth (Ma) above.

In Sumerian culture
In the city of Eridu, Enki's temple was known as E2-abzu (house of the deep waters) and was located at the edge of a swamp, an abzu. Certain tanks of holy water in Babylonian and Assyrian temple courtyards were also called abzu (apsû). Typical in religious washing, these tanks were similar to Judaism's mikvot, the washing pools of Islamic mosques, or the baptismal font in Christian churches.

In Sumerian cosmology
The Sumerian god Enki (Ea in the Akkadian language) was believed to have keen eyes and appeared out of the abzu since before human beings were created. His wife Damgalnuna, his mother Nammu, his advisor Isimud and a variety of subservient creatures, such as the gatekeeper Lahmu, also lived in the abzu.

As a deity
Abzu (apsû) is depicted as a deity only in the Babylonian creation epic, the Enūma Eliš, taken from the library of Assurbanipal (c. 630 BCE) but which is about 500 years older. In this story, he was a primal being made of fresh water and a lover to another primal deity, Tiamat, a creature of salt water. The Enūma Eliš begins: "When above the heavens (e-nu-ma e-liš) did not yet exist nor the earth below, Apsu the freshwater ocean was there, the first, the begetter, and Tiamat, the saltwater sea, she who bore them all; they were still mixing their waters, and no pasture land had yet been formed, nor even a reed marsh." This resulted in the birth of the younger gods, one, Enki, would later contain Apsu when he plotted to kill them because of their noise. Enraged, Tiamat gives birth to monsters, filling their bodies with "venom instead of blood", and made war upon her treacherous children, only to be slain by Enki's son Marduk, the god of Storms, who then forms the heavens and earth from her corpse.

In popular culture
Abzû is a 2016 adventure game that was influenced by Sumerian mythology of Abzu.