The Central Asian river system that includes the Naryn and historically flows toward the Aral Sea is the Syr Darya.
The Syr Darya begins where the Naryn and Kara Darya meet in Uzbekistan’s part of the Fergana Valley. It then flows northwest through Uzbekistan and southern Kazakhstan before reaching the northern remnants of the Aral Sea. The Naryn is therefore a headstream, rather than a separate answer to the whole system.
Known in antiquity as the Jaxartes, the river was important to the history of Central Asia. Greek and later Islamic sources used forms of that older name, and settlements along its course connected trade routes, irrigated farmland, and frontier zones.
The Syr Darya is one of the Aral Sea basin’s two principal rivers; the other is the Amu Darya. Soviet-era irrigation diverted enormous volumes for cotton and other crops, contributing to the Aral Sea’s dramatic shrinkage. That environmental history is why older descriptions say the river flowed into the Aral Sea, even though its modern endpoint is greatly altered.