Enki 𒂗𒆠 / YAH
According to ancient Sumerian mythology, the Tigris and Euphrates flow from the shoulders of Enki 𒂗𒆠 / EYAH (i.e. the "YHVH"), for he is the head of the rivers, the 'source', et cetera. The name YAH comes from the ancient Akkadian name “EA” which means "Life", and is derived from the Semitic root HYY meaning "life", which can also mean "spring" or "running water", as in to say the “Fountain of Life”.
The evolution of the name ENKI to YAH took place between the Sumerian and Akkadian languages, both of which used cuneiform writing, but had different pronunciations. Thus the Sumerian 𒂗𒆠 (“Enki”) became the Akkadian “EA”, which is pronounced “YAH”.