The River Tees, in England, rises on the eastern slope of Cross Fell in the North Pennines and flows eastwards for 85 miles (137 km) to reach the North Sea in the North East of England. The modern day history of the river has been tied with the industries on Teesside in its lower reaches, where it has provided the means of import and export of goods to and from the North East England. The need for water further downstream also meant that reservoirs were built in the extreme upper reaches, such as Cow Green.

Cross Fell is the highest mountain in the Pennines of Northern England and the highest point in England outside the Lake District. It is located in the North Pennines Area of Outstanding Natural Beauty. It lies within the county of Cumbria and the historic county boundaries of Cumberland.