The motorway dam spans the Deanhead Valley in the Pennines between Huddersfield and Rochdale and the main contractor for the project was Sir Alfred McAlpine & Sons.

[2] Deanhead village was submerged and many buildings demolished to make way for the reservoir but the church remains and its vicarage is used by the sailing club.

[3] Both the church and adjacent school were at risk of slipping down the hillside into the dam and were not used after 1971 when the motorway opened.

The reservoir started to fill in July 1969 and the area was landscaped and parking and other facilities were provided.

[3] The motorway, which was dependent on the completion of the dam, was opened to traffic on 20 December 1970 and officially opened by Queen Elizabeth II who unveiled a plaque near the valve tower of Scammonden Water on 14 October 1971.