For 20 points, name this only navigable river of Iran.
This river is home to the dam with the largest spillway gates in the world, the Masjed-Soleyman Dam, as well as the Gotvad Dam. A UNESCO World Heritage Site which lies on this river is the "Band-e-Kaiser," or Caesar's Dam, which was supposedly constructed by the army of the Roman Emperor Valerian after its defeat at the hands of Shapur I. This river originates in the Zard Kuh mountains of the Zagros Range and flows through Khuzestan. Along with the Tigris, Euphrates, and Karkheh, it is believed to be one of the four rivers of Eden in the Bible, being identified with the Pishon. The city of Basra was forced to declare a state of emergency after dams built on this river raised the salinity level of the Shatt-al-Arab. For 20 points, name this only navigable river of Iran.
This river is home to the dam with the largest spillway gates in the world, the Masjed-Soleyman Dam, as well as the Gotvad Dam.
Karun River