(also Styr), a river in L’vov, Volyn’, and Rovno oblasts, Ukrainian SSR and Brest Oblast, Byelorussian SSR; a right tributary of the Pripiat’ River of the Dnieper River basin. The Styr’ measures 494 km in length and drains an area of 12,900 sq km. It originates in the Podol’e Upland and flows through the Volyn’ Hills and, in its lower course, through the Poles’e Lowland. It is fed mainly by snow. High water lasts from March to May. The mean flow rate 168 km from the mouth is 45 cu m per sec. The river freezes, as a rule, in December, sometimes even in early March; the ice breaks up between late February and early April. The lower course is navigable. The city of Lutsk is situated on the Styr’.