(also Uda), a river in Kharkov Oblast, Ukrainian SSR; a right tributary of the Severskii Donets. The Udy is 164 km long and drains an area of 3,890 sq km. It originates in Belgorod Oblast, RSFSR, on the southwestern slopes of the Central Russian Upland. It is fed mainly by snow. The upper Udy dries up for a period of 4½ months. The mean flow rate 42 km from the mouth is about 11 cu m per sec. The river freezes between October and January and opens up between late February and early April. The city of Kharkov is situated at the confluence of the Kharkov, Lopan’, and Udy rivers.