Genesis 2:10 And a river went out of Eden to water the garden; and from thence it was parted, and became into four heads. 11 The name of the first is Pison:
The Hebrew text could be interpreted to mean that the rivers start elsewhere and all meet in Eden. This feels correct.
There are lots of guesses to which river was the Pishon. 2 of the other 4 are known.
Hidekel {the Tigris},
Phrath { the Euphrates },
and Gihon)
Hidekel {the Tigris},
Phrath { the Euphrates },
and Gihon)
Possible Rivers that could be Pishon: