Khuzestan has great potential for agricultural expansion, which is almost unrivaled by the country's other provinces. Large and permanent rivers flow over the entire territory contributing to the fertility of the land. Karun, Iran's most effluent river, 850 kilometers long, flows into the Persian Gulf through this province. The agricultural potential of most of these rivers, however, and particularly in their lower reaches, is hampered by the fact that their waters carry salt, the amount of which increases as the rivers flow away from the source mountains and hills. In case of the Karun, a single tributary river, Rud-i Shur ("Salty River") that flows into the Karun above Shushtar contributes most of the salt that the river carries. As such, the freshness of the Karun waters could be greatly enhanced if the Rud-i Shur could be diverted away from the Karun. The same applies to the Jarahi and Karkheh in their lower reaches. Only the Marun is exempt from this.