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Welcome to Anglesey

Aerial image of the Menai Strait showing Menai bridge in foreground and Brittania bridge behind

Menai Strait

Aerial image of the Menai Strait showing Menai bridge in foreground and Brittania bridge behind

The Menai Strait is the captivating submerged valley that separates Anglesey from mainland North Wales.

The Menai Strait is the captivating, submerged valley that separates Anglesey from mainland North Wales. It is orientated northeast to southwest and stretches for approximately 15 miles from Trwyn Penmon to Abermenai Point. It encompasses numerous habitats, ranging from dynamic marine reefs to expansive sandy beaches and lofty sea cliffs.

The area forms part of the Menai Strait and Conwy Special Area of Conservation (SAC). This is a designation which enables the protection of special habitat types and species (excluding birds) which are considered to be most in need of conservation at a European level. The environmental conditions of the Menai Strait are unusual, inasmuch as it is sheltered from wave action but subject to rapid tidal flows which can reach speeds of 4 metres per second during spring tides. There is also much suspended matter in the water, which creates ideal conditions for filter feeders.

The Strait’s inner shores are dominated by bristle worms such as Spio filicornis. The limestone reefs are home to several rock-boring species including rock-boring sponges, piddocks and acorn worms. Large colonies of breadcrumb sponges exist, accompanied by other reef dwellers including scorpion spider crabs, red-eyed velvet swimming crabs, butterfish, lumpsuckers, and conger eels. The Straits are home to a wide variety of shore and wading birds, such as little egret, oystercatcher, curlew and redshank.

During some winters, internationally important flocks of common scoter have been observed, gathering to feed upon the plentiful populations of bivalve molluscs. The nationally scarce dwarf eelgrass Zostera noltii is found in the area between Beaumaris and Lleiniog. If you are lucky, you may catch a glimpse of a seal or harbour porpoise hunting and playing in the tidal races.


The Menai Strait, or Afon Menai as it is known locally, is the sea channel that separates Anglesey from mainland Gwynedd. It is connected to the mainland by Thomas Telford’s Menai Suspension Bridge and Robert Stephenson’s Britannia Bridge. The Strait varies in width from about 300m to three quarters of a mile. The central region (between the two bridges) is known as the ‘Swellies’; this is a unique environment with a strong, reversing tidal flows, rapid currents and swirling whirlpools. The Strait also has many small, offshore islands, of which there are good views from the bridges. From the Anglesey side, there are lovely views of the Snowdonia and Carneddau mountain ranges, Conwy Bay and the towns of Bangor through to Caernarfon.

The Strait is a major geological fault, forming a transition between Anglesey and the similar-aged, but apparently unrelated, rocks of North Wales.

It was carved by ice. This unmistakeable feature was formed by glaciers flowing from Snowdonia, and by the Irish Sea ice stream which covered Anglesey during the last ice age approximately 22,000 years ago (

The Strait is also a marine Special Area of Conservation (SAC), with a rich variety of habitats including sea inlets and estuaries, mud and sand flats, lagoons, salt marsh, shingle beaches, sea cliffs and submerged limestone reefs.

Particular highlights along the Menai Strait include the Newborough Warren sand dune complex, the Swellies with the backdrop of Telford’s Menai Bridge and the Carneddau, and Beaumaris, Penmon and Black Point.



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Menai Bridge, Anglesey


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