Teesside is a built-up area around the River Tees in North East England, split between County Durham and North Yorkshire. The area contains the towns of Middlesbrough, Stockton-on-Tees, Billingham, Redcar, Thornaby-on-Tees, and Ingleby Barwick. Teesside's economy was once dominated by heavy manufacturing until deindustrialisation in the latter half of the 20th century. Chemical production continues to contribute significantly to Teesside's economy.

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.