What is the longest river in central asia, and which countries does it border

Amu River to the East it borders China Pakistan to the South  

The longest river in Central Asia is the Amu Darya. It serves as the border between Afghanistan and Tajikistan, and in part between Uzbekistan and Turkmenistan.

The river forms at the confluence of the Vakhsj and Pandzh rivers in Tajikistan, and flows northwest across the Turan basin until it reaches the Aral Sea in Uzbekistan. It is 1415 km long, calculated from the confluence of Vakhsj, and 2540 km from the source in Pamir.