Difference the reservoir has made
Cow Green continues to supply water to thousands of homes and industries in Teesside to this day.
The expensive and protracted disputes in the years before the reservoir was built were viewed as contributing to a growing mistrust between the water industry and environmentalists.
How the reservoir was built
Cow Green reservoir was created by building a dam at the point where a flat area of the river Tees crossed land near an old mine. The mine was previously dug for barium sulphate – a mineral used for making paint.
The first day's work on the project started with a bang when Sir Charles Allison, chairman of the local water board, hit the plunger on a detonator. This set off an explosion which blew a crater on the reservoir site.
Sir Charles may have chosen this violent start to the project to make a point. He was infuriated that environmental campaigners had delayed the reservoir for nearly 10 years.
The next 4 years saw engineers build the 25m high, 550m long dam to hold back 40,000m litres of water.
The project team paid close attention to the design of Cow Green's core following erosion problems with the clay core of recently completed Balderhead reservoir.
Engineers decided on sand drains for Cow Green as they thought this would cut down seepage from the reservoir. Sand drains use small particles to filter impurities from water.
Around 300 people made up the construction team.