Mandaeism
The religion has been practised primarily around the lower Karun , Euphrates and Tigris and the rivers that surround the Shatt-al-Arab waterway , part of southern Iraq and Khuzestan Province in Iran . 
<triplet> Shatt-al-Arab <subj> Karun <obj> tributary <subj> Euphrates <obj> tributary <subj> Tigris <obj> tributary