That's really difficult to say. Mesopotamia is a region that was comprised of many different people with hundeds of gods total.
there is no MAIN god that Mesopotamia people believe in, that is why they are polytheims.
gaea
If you mean the Sumerians, I think they were into the Sun god who warms all but what religion not a god
Marduk was the original god of agriculture in Mesopotamia mythology.
the main gods name is hutzlopochtli
Anatu, Minlil, and Ki were the Goddesses of the in Mesopotamia. Ellil was the God of the earth and wind.
sun god
The main was the sun god - Huitzilopochtli. All the gods were important to the Aztecs but the sun god was the most powerful.
Marduk
Spaves
Huitzilopochtli - the sun god of Aztecs
The two main rivers for Mesopotamia are the Euphrates and the Tigris.