In 1925, members of the North Wales and South Cheshire Joint Electricity Authority visited the dam at Maentwrog, then under construction.

It has an area of 2 square miles (5.2 km2) and can hold 33,000,000 cubic metres (1.2×109 cu ft) of water.

[3][2] By 1925, the transmission lines of the North Wales and South Cheshire Joint Electricity Authority to which the North Wales Power Company was connected extended from Pwllheli to Runcorn and to the borders of Staffordshire, and served an area of 1,200 square miles (3,100 km2).

In the year 1935/6, the North Wales Power Company noted that rainfall was well above average, with 144.4 inches (3,670 mm) of rain at Cwm Dyli.

As a result, the company's three stations (Maentwrog, Cwm Dyli and Dolgarrog) were able to generate a total of 93,199,950 MWh of electricity.

[8] Maentwrog power station has been owned by the following organisations, through nationalisation, reorganisation and privatisation of the electricity industry.

From 2004, the Nuclear Decommissioning Authority (NDA) assumed ownership although operations are devolved to NDA site licence company Magnox Ltd.[6] The original generating plant comprised four 6 MW Boving-English Electric 6.6 kV generating sets.