An Act of Parliament was passed in 1892 for The Birmingham Corporation to compulsory purchase the water catchment area of the Elan and Claerwen Valleys.
In 1893 the building work began, 100 occupants of the Elan Valley had to move, only the landowners received compensation payments. Many buildings were demolished, 3 manor houses, 18 farms, a school and a church. Six reservoirs were to be built with Caban-Coch, Penygarreg and Craig Goch in the Elan Valley and Dol-y-mynach, Ciloerwynt and Pant-y-beddau in the Claerwen Valley.
The first phase of building, Caban Coch, Garreg Ddu, Pen y Garreg, Craig Goch dams were completed with the foundations of Dol y Mynach dam along with Dol y Mynach Tunnel which supplies water from the Clearwen Valley to Garreg Ddu reservoir and the 73-mile aqueduct to the Frankley reservoir, near Birmingham were all built by 1904. On 21st July 1904 King Edward VII and Queen Alexandra opened the Elan dams and water started flowing along 73 miles of pipeline to Birmingham.
The building of the second phase dams was delayed due to the 1st and 2nd World Wars and work didn't start again till 1946. With advancements in engineering only one large dam (Claerwen Dam) was needed rather than 3 smaller ones in the Claerwen Valley. Claerwen Dam was opened by Queen Elizabeth on 23rd October 1952.