The Gihon was one of the 4 rivers that flowed out of Eden thought to be located in Mesopotamia. It was also thought to encircle the entire land of Cush which is thought to be modern day Ethiopia. I have read in places that Ethiopians called the river the blue Nile. If that is true then you would be right. That Gihon is thought to no longer exist. A very interesting concept. I love this stuff.