Landscapes & nature
Lake Vyrnwy
Reservoir in Wales which supplies water to Liverpool
Wikipedia names Lake Vyrnwy as where 2 films and series were filmed; each title’s page links to the sentence that says so. Wikidata records no shoot here yet.

Filmed here, per Wikipedia
Wikipedia says these were filmed in Lake Vyrnwy. Each title’s page links to the sentence that says so.
Filming locations nearby
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Landscapes & nature Pistyll Rhaeadr
Wales · 11 km north-east
Waterfall in Powys, Wales, UK
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Towns & cities
Llanrhaeadr-ym-Mochnant
Wales · 15 km north-east
Village and community in Powys, Wales
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Landscapes & nature
River Dee
United Kingdom · 19 km west
River in England and Wales
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Towns & cities
Llansilin
Wales · 23 km east
Village and community in Powys, Wales
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Towns & cities
Corris
Wales · 27 km south-west
Village and community in Gwynedd, Wales, UK
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Landscapes & nature
Snowdonia
Wales · 27 km north-west
Mountainous area in Wales