NO ONE REALLY KNOWS
The eygptians of mesopotamia used the Tigris and Euphrates for their crops the only problem was the rivers flooded in harvest season and there wasn't enough water for planting season but this problem...
It is Tigris River. Refer to related question for more information.
The Euphrates River originates in Turkey, passes through Syria and Iraq, and discharges in the Arabian (or Persian) gulf.
Western Asia; Begins in Turkey and ends into the Persian gulf. Runs through Syria and Iraq.
People don't live in rivers. Try asking the population of a city around the Euphrates and Tigris rivers