evidence: The Shatt al-Arab River (SAR) is a transboundary river between Iraq and Iran. The bulk of it has traditionally been under Iraqi jurisdiction, yet Iran has always held significant influence. This paper applies the framework of hydro-hegemony to distinguish between two different hegemonic configurations operated over SAR. In the first period, Iran exercised coercive tactics, prompting Iraq to sign the Algeria Accord in 1975. However, after four years, the eight-year war between the two states revoked this institutional order, paving the way for a new era. During this period, which began dominantly after 2003, Iran exerted soft power. The Iranian Islamic regime manipulated ties with Iraqi elites to influence the course of Iraqi policy. Nonetheless, by helping Iraqis defeat ISIS and curbing the Kurdish issues following their referendum to separate from Iraq in 2017, Iran ensured the majority of Iraqis' willing acquiescence. Consequently, it contained SAR on its own terms. [...] Al-Jaffal, O. (2019) Will Iraq lose its benefits from Shatt al-Arab river to Iran? Al-monitor the Pulse of the Middle East. 23 March 2019. Retrieved from: https://www.al-monitor.com/pulse/originals/2019/03/iran-iraq-shatt-al-arab.html (accessed 8 September 2018). [...] Khalil, S. 2018. The taluk line creeps towards Iraq and takes hold of Shatt al-Arab, Rawabet Center for Research and Strategic Studies. Retrieved from https://rawabetcenter.com/en/?p=5307 (accessed 4 March 2020)