The Syr Darya /ˌsɪər ˈdɑːrjə/ SEER-DAR-yə,[a][b] historically known as the Jaxartes (/dʒækˈsɑːrtiːz/ jak-SAR-teez, Ancient Greek: Ἰαξάρτης), is a river in Central Asia.

It is the northern and eastern of the two main rivers in the endorheic basin of the Aral Sea, the other being the Amu Darya (Jayhun, also known by its classical name the Oxus).

The earliest recorded name was Jaxartes or Iaxartes (Ἰαξάρτης) in Ancient Greek, consist of two morpheme Iaxa and artes, found in several sources, including those relating to Alexander the Great.

[9] When the Macedonian army of Alexander the Great reached the Jaxartes in 329 BC, after travelling through Bactria and Sogdia without encountering any opposition, they met with the first instances of native resistance to their presence.

As the revolt against Alexander intensified it spread through Sogdia, plunging it into two years of warfare, the intensity of which surpassed any other conflict of the Anabasis Alexandri.

[12] In 2012, the Syrdarya–Turkestan State Regional Natural Park was opened in Kazakhstan, in hopes of protecting the river plain ecosystems, archaeological sites, and historical-cultural monuments, as well as plants and animal species, some of which are rare or endangered.

Along its course, the Syr Darya irrigates the most productive agricultural regions in all of Central Asia, together with the towns of Kokand, Khujand, Kyzylorda and Turkestan.

Massive expansion of irrigation canals in Middle and Lower Syr Darya during the Soviet period to water cotton and rice fields caused ecological damage to the area.