a tributary of the Don River, southwestern Russia and eastern Ukraine. The Donets is 650 miles (1,050 km) long and drains a basin of 39,000 square miles (100,000 square km). Rising in the Central Russian Upland, it flows south past Belgorod, Russia; enters Ukraine and passes to the east of Kharkiv; swings southeastward and eventually reenters Russia; and then turns south to join the Don below Konstantinovsk. The river is frozen from early December to late March. It follows a course along the north of the Donets Basin industrial region, which uses much of its water and causes severe pollution problems. A water shortage in the river and industrial area led to the construction in the 1970s of a canal carrying additional supplies from the Dnieper to the Donets. Six weirs make navigation possible upstream to Donetsk in Rostov oblast (province).