IT put Huddersfield on tap and linked both sides of the Pennines.
And today it has been a massive landmark for 40 years.
While millions of motorists cross Scammonden Dam every month, few consider the incredible work which went into building one of Britain’s greatest feats of engineering.
To celebrate 40 years of the dam, reservoir owner Yorkshire Water is carrying out £220,000 of improvements to encourage the public to visit one the country’s most impressive – and useful – structures.
Footpaths to and around the reservoir are currently being improved to allow wheelchair and pushchair access.
A nature trail and a viewing platform giving spectacular vistas of the reservoir and Deanhead Valley are also in the pipeline.
Yorkshire Water countryside and recreation manager Alastair Harvey said: “We want to welcome our customers to Yorkshire Water land. Many millions of people drive over it and don’t give a second thought to the technical-ities behind building it.
“We want people to come and bring their friends and family and see what we have to offer.”
Scammonden Dam, which was officially opened by the Queen on this day in 1971, solved two problems.
It provided a fast link on the M62 between Yorkshire and Lancashire, now Greater Manchester.
And the dam and 4,200 sq metre reservoir behind it provided a regular water supply for Huddersfield and its surrounding area.
Scammonden Dam was designed as part of the M62 in the early 1960s.
It was designed by engineer Bill Jollans, who had been appointed as manager of the Huddersfield Corporation Waterworks in 1962.
Mr Jollans, who had lived at Lake House, next to Blackmoorfoot reservoir, died in 2007.
The excavation of Deanhead Valley began in August 1964, followed by excavations for the dam in 1966.
Large quantities of peat had to be removed to provide a stable base for the dam.
Water started to fill the reservoir in July 1969 and by October it held 7.7 million cubic metres.
The M62, including Scammonden Dam, was opened to traffic on December 20, 1970.
At the dam and reservoir’s official opening on October 14, 1971, the Queen unveiled a plaque near the valve tower of Scammonden Water.
A roundabout, which was built for the royal motorcade, remains.
The reservoir supplies water to about 200,000 people in the Huddersfield area, although water can be pumped to anywhere around Yorkshire.
Scammonden Water is just over 2,000ft (625 metres) long.
When full the reservoir has a surface area of 4,200 sq metres.
It is 240ft (73 metres) deep at its deepest point.
Scammonden Water stores up to 1,730 million gallons of water.
The dam is 230ft (70 metres) tall and almost a mile long.
Water from the reservoir is routed to water treatment works and other reservoirs in the area, including at Longwood and Butterley Reservoir, near Marsden.