Tryweryn flooding

The Tryweryn flooding, or Tryweryn drowning (Welsh: Boddi Tryweryn), was the 1965 flooding of the Tryweryn valley in Gwynedd (then Merionethshire), Wales, to create the Llyn Celyn reservoir. The flooding of the valley, located to the north west of Bala, submerged the rural community of Capel Celyn. The project was developed by Liverpool Corporation, to supply Liverpool and Wirral with water for industry.

The flooding was and remains controversial in Wales. Capel Celyn was one of the last Welsh-only speaking communities in the area. The flooding was opposed by 125 local authorities, and the site and Liverpool was the location of protests. The parliamentary bill establishing permission for the reservoir received no support from Wales' 36 members of Parliament, with members mainly opposing and a few abstaining, however the bill passed overall.

Failed efforts to prevent the flooding despite strong opposition in Wales has attributed the flooding with leading to a rise in support for the Welsh nationalist party Plaid Cymru, and increasing powers and responsibility to Wales, culminating in Welsh devolution, although water is not fully devolved to Wales.

The event has inspired various media, particularly the Cofiwch Dryweryn mural. Liverpool City Council formally apologised in 2005.