Khopyor (Russian: Хопёр, also transliterated as Khoper) is a river in European Russia, the biggest left tributary of the Don River. It is 979 kilometres (608 mi) long, with a watershed of 61,100 square kilometres (23,600 sq mi). The mouth width is 300 metres (980 ft). The Khopyor is navigable up to 323 kilometres (201 mi) from the mouth. The maximum discharge is 3,720 cubic metres per second (131,000 cu ft/s); the average discharge is 150 cubic metres per second (5,300 cu ft/s), and the minimum discharge is 45 cubic metres per second (1,600 cu ft/s).
According to legend, an oldman Hopper lived in these places of Penza Oblast. One day he went by steppe and saw 12 springs. The old man took a shovel and assembled all the springs in one big stream. On this stream oldman Hopper built a mill to grind grain for the peasants from nearby villages. Later the river was given the name of its creator.