Cors Gyfelog National Nature Reserve is a wetland site near the village of Pant Glas in the community of Clynnog, Gwynedd, Wales. It is important as a habitat for the Marsh Fritillary butterfly, as well as Lesser Redpoll and Grasshopper Warbler.

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• Cors Gyfelog National Nature Reserve, near Caernarfon, North Wales
• Corsydd Eifionydd - Special Areas of Conservation