Kenfig Pool (Welsh: Pwll Cynffig) is a national nature reserve situated near Porthcawl, Bridgend.
Wild storms and huge tides between the 13th and 15th centuries are mainly responsible for creating the Kenfig dunes near Porthcawl, as they threw vast quantities of sand up over the Glamorgan coast.
Kenfig Pool lies at the heart of the national nature reserve and is a valuable stopping point for migrating birds.
An island, built by the aristocrats living in nearby Margam to encourage wildfowl (which they would shoot) to nest there, has long since sunk beneath the waters.
An old, yet popular theory claims that the lake was created during a "sinking of the land" in a massive earthquake, but has since been rejected as downright bizarre.
When historian Rhys Merrick visited during the time of Elizabeth I, and enquired about a lost medieval town in the vicinity, some told him (correctly) that it lay near the castle, but others said it had "sinked and become a great mere" - Kenfig Pool.
In the morning, when the country folk rushed to Kenfig, they found nothing left of the city, and a huge lake in its place.