Menai Strait

The Menai Strait (Welsh: Afon Menai, the "River Menai") is a narrow stretch of shallow tidal water about 25 km (16 mi) long, which separates the island of Anglesey from the mainland of Wales.

The strait is bridged in two places – the main A5 road is carried over the strait by Thomas Telford's iron suspension bridge, the first of its kind, opened in January 1826, and adjacent to this is Robert Stephenson's 1850 Britannia Tubular Bridge. Originally this carried rail traffic in two wrought-iron rectangular box spans, but after a disastrous fire in 1970, which left only the limestone pillars remaining, it was rebuilt as a steel box girder bridge, and now carries both rail and road traffic (A55). Between the two bridge crossings there is a small island in the middle of the strait, Ynys Gorad Goch, on which are built a house and outbuildings and around which are the significant remains of fish traps, no longer used.

The strait varies in width from 400 metres (1,300 ft) from Fort Belan to Abermenai Point to 1,100 metres (3,600 ft) from Traeth Gwyllt to Caernarfon Castle. It then narrows to about 500 metres (1,600 ft) in the middle reaches (Y Felinheli and Menai Bridge) and then it broadens again. At Bangor, Garth Pier, it is 900 metres (3,000 ft) wide. It then widens out, and the distance from Puffin Island (Welsh: Ynys Seiriol) to Penmaenmawr is about 7.5 kilometres (4.7 mi). The differential tides at the two ends of the strait cause very strong currents to flow in both directions through the strait at different times, creating dangerous conditions. One of the most dangerous areas of the strait is known as the Swellies (or Swillies – Welsh Pwll Ceris) between the two bridges. Here rocks near the surface cause over-falls and local whirlpools, which can be of considerable danger in themselves and cause small boats to founder on the rocks. This was the site of the loss of the training ship HMS Conway in 1953. Entering the strait at the Caernarfon end is also hazardous because of the frequently shifting sand banks that make up Caernarfon bar. On the mainland side at this point is Fort Belan, an 18th-century defensive fort built in the times of the American War of Independence.

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