Situated to the south-west of Caernarfon, Y Foryd is a partially enclosed intertidal bay on the Menai Strait. This unusual coastal inlet was formed by the subsequent interacting processes of sea level rise, coastal erosion and tidal deposition.
Being so sheltered from wave action, the bay contains a great diversity of inter-tidal sediments and substrates which are inhabited by diverse communities of benthic invertebrates.
Together with the Menai Strait and Colwyn Bay it is part of a European Special Area of Conservation in recognition of the importance of this habitat.
The rare Dwarf Eelgrass occurs in parts of the inter-tidal estuary and is food to wildfowl such as Brent Geese and Widgeon. Stands of Sea Cord-grass provide good cover for wildfowl in the innermost area of the bay. To the western side, extensive saltmarsh has good shows of flowering Sea Aster in late summer.
Over 200 bird species have been recorded around Y Foryd. Mute Swan, Little Egret, Shelduck, Oystercatcher and Curlew are usually conspicuous all year. Ringed-Plover, Turnstone (non-breeders), and Redshank may also be seen year-round. The RSPB is managing the wet pastures on its nearby Morfa Dinlle Nature Reserve to encourage the breeding of Lapwings. However, the estuary is most especially known for its wintering wildfowl. Rafts of up to 5000 Wigeon are a special feature of winter, usually with Goldeneye and Red-breasted Merganser, and often wading Greenshank and Bar-tailed Godwit.
Because it is at the entrance to the Menai Strait, and at its narrowest crossing-point, Foryd Bay has always been of strategic importance. In the Iron-Age, 2,500 years ago, the double earth ramparts of Dinas Dinlle held a commanding position on the Irish Sea coast. According to the Mabinogi, it was here that the warrior and magician, Lleu Llaw Gyffes was raised.
The late 18th Century Fort Belan was built at the tip of the Dinlle Peninsula to defend the Strait at the time of the American War of Independence and then the Napoleonic Wars. The Fort was used again during the Second World War when all three armed services had stations here. The Royal Air Force dominated the scene and developed what is now Caernarfon Airport. To this day the fort and its dock remain largely as originally constructed, and is now a popular residential-holiday venue.
Glaciation deposited the boulder-clays which now form the low cliffs around Dinas Dinlle.