a river in the Kuibyshev and Saratov oblasts of the RSFSR; a left tributary of the Volga. The Bol’shoi Irgiz is 675 km long, drains a basin of 24,000 sq km, rises in a spur of the Obshchii Syrt, flows through a broad valley, and discharges into the Volgograd Reservoir. It is fed primarily by snow. Its waters are used for irrigation. The city of Pugachev is located on the river.