Greenbooth Reservoir took over two years to build and was completed in 1961, at a cost of £2,101,000. It was planned and built by the Heywood and Middleton Water Board. The dam itself is at the southern end of the Naden valley and it is the lowest of four reservoirs built in the valley. The dam is 117 feet high and 1,000 feet long
It is built on a concrete foundation trench and has a central core of natural puddle clay, which is watertight whilst retaining the ability of moving without cracking. The clay was laid in the traditional method – by men walking about upon it and trampling it with the heels of their boots (much as you would heel in a plant in a garden). On the upstream side of the builders used a harder shale that allowed the clay core to stay damp, and on the other side of the dam they used a more compact kind of sub-soil, in order to stiffen the sloping embankment. Fissures in the rock along the reservoir sides had to be sealed before it could begin to be filled.
The tunnel carrying the main outlet and overflow pipes was completed in 1961. Water from Greenbooth is piped to the filter house at Clay Lane reservoir, where it is purified for domestic use. The reservoir increased the supply of water in the Heywood & Middleton areas by 7000,000,000 gallons.
There was a problem with the dam in 1983 when it was reported that the dam appeared to be sinking. A round-the-clock watch was kept on the dam wall and 25 million gallons per day were drained from the reservoir to relieve pressure on it. Repairs were carried out and by 1986 the reservoir was full again.
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