How many places does the river tees run through?

River Tees, river in northeastern England, rising on Cross Fell in the northern Pennines and flowing 70 miles (110 km) east to the North Sea. It forms the boundary between the historic counties of Yorkshire and Durham. In its upper course the Tees flows in a typical Pennines dale (valley) where high moorlands flank an attenuated strip of farmland. At Caldron Snout and High Force there are waterfalls where the river crosses the hard dolerite outcrop of the Whin Sill. Below Middleton-in-Teesdale the valley broadens, and the river receives important right-bank tributaries-the Lune, the Balder, and the Greta-from subsidiary dales.