The Hawizeh Marshes are a complex of marshes that straddle the Iran–Iraq border. The marshes are fed by two branches of the Tigris River in Iraq and the Karkheh River in Iran. The Hawizeh marsh is critical to the survival of the Central and Hammar marshes also make up the Mesopotamian Marshes, because they are a refuge for species that may recolonize or reproduce in other marshlands. Hawizeh Marshes are drained by the Al-Kassarah. This river plays a critical role in maintaining the marshes as a flow-through system and preventing it from becoming a closed saline basin.