The Sepid-Rud (; ; also known as Sefid-Rud) is a river, approximately long, rising in the Alborz mountain range of northwestern Iran and flowing generally northeast to empty into the Caspian Sea at Rasht.
Other names and transcriptions include Sepëd-Rà «d, Sefidrud, Sefidrood, Sepidrood, and Sepidrud. Above Manjil, "Long Red River".
William Smith equated the river with the Amardus () or Mardus (ÃÂìÃÂôÿÃÂ) river of antiquity.
The river is historically famous for its abundant fish, especially the Caspian trout, Salmo trutta caspius.
The Sefid-Rud has cut a water gap through the Alborz mountain range, the Manjil gap, capturing its two headwater tributaries, the Qizil ÃÂzan and Shahrood rivers. It then widens the valley between the Talesh Hills and the main Alborz range. The gap provides a major route between Tehran and GëlÃÂn Province with its Caspian lowlands.
In the wide valley before the Sefid-Rud enters the Caspian Sea, a number of transportation and irrigation canals have been cut; the two biggest are the Khomam and the Now.
The Sefid-Rud was dammed in 1962 by the Shahbanu Farah Dam (later renamed Manjil Dam), which created a reservoir and allowed the irrigation of an additional . The reservoir mediates some flooding and significantly increased rice production in the Sefid Rud delta. The hydroelectric component of the dam generates 87,000 kilowatts. The completion of the dam had a negative impact on the river's fisheries, through reduced stream flow (due to diversion), increased water temperature, and decreased food availability, especially for sturgeon but also for the Caspian trout.
The river was known in antiquity as Mardos (; ) and Amardos (; ). In the Hellenistic period, the north side of the Sefid (then Mardus) was occupied by the Cadusii mountain tribe .
David Rohl proposes identification of Sefid-Rud with the Biblical Pishon river.