The Helmand River, which originates in Afghanistan and flows into Iran, has been the subject of dispute due to water sharing and usage rights between the two countries.
Step 1: Importance of the Helmand River
It is a critical water source for irrigation and drinking in both nations.
Step 2: Nature of dispute
The disagreement centers on dam construction and water diversion by Afghanistan, affecting Iran’s water supply downstream.
Hence, option (D) is the correct answer.