Tees

Tees, river in Cumbria, Durham, North Yorkshire, and Cleveland, north-eastern England. The river rises on Cross Fell in the northern Pennines and flows south-east through high moorland and over waterfalls at Caldron Snout and High Force; its valleys broaden out below Middleton-in-Teesdale in County Durham. The river then forms the border with North Yorkshire until just above Yarm, where it turns north-east into Cleveland and via an 8-km (5-mi) estuary into the North Sea below Middlesbrough. Below Stockton-on-Tees, its course has been artificially straightened and land reclaimed; until the 19th century the area of its estuary consisted of shifting mud flats.

The Tees, linked to the River Tyne, formed the basis of England’s first regional water grid system. The river’s tributaries include the Lune, Balder, and Greta; its length is 128 km (80 mi), only navigable as far as Stockton-on-Tees, about 11 km (7 mi) from the sea; its drainage basin is about 2,110 sq km (815 sq mi).