Ramsey Island ( Welsh : Ynys Dewi ) is an island about 1 km off the coast of St David’s peninsula in Pembrokeshire on the northern side of St Brides Bay , in southwest Wales . It is 640 acres (259.00 hectares) in area.
In Welsh the island is named after St. David ( Dewi Sant ), patron saint of Wales . It was the home of his confessor, St. Justinian . The nearest town, strictly a city , is St David’s .
Ramsey Island is less than 3.2 km (2 mi) long and its highest point is 136 meters (446 ft) above sea level at Carnllundain , and is listed as a HuMP . It is the fourth largest island in Wales , after Anglesey , Holy Island and Skomer . 
The island has a different geology for a relatively small area; it includes sedimentary , volcanic and intrusive igneous rocks dating from the early Palaeozoic Era. The larger part of the island is formed from the mudstones of the Tetragraptus Mudstone Formation (also known as the ‘Penmaen Dewi Shale Formation’ and again as the ‘Uchaf Formation Road’ (sic) after the Rhod Uchaf locality on the island’s east coast). However Carnysgubor stands proud of them as a result of a more resistant microtoniteintrusion. In contrast the coastal cliffs between Trwyn-drain-and Trwyn-Sion-Owen and Trofyn Ogof Hen and Rhod Uchaf are formed by sedimentary rocks, the mica-rich Lingula Flags and the sandstones and mudstones of the Ogof Hen Formation. The rock strata are typically steeply tilted and commonly faulted .
Running NW-SE across the center of the island from Aber Mawr to the vicinity of the Bitches is a band of late Arenig age tuffs and ‘pencil slates’ assigned to the Abermawr Formation. Its boundary with the sediments to the north is a fault.
The south of the island is dominated by a rhyolite intrusion as its southern coast. To the west of the Ramsey Fault which runs from Aber Mawr to Porth Lleuog, is Carnllundain which is formed from the tough rhyolitic tuffs of the Carn Llundain Formation. These tuffs arose as volcanic ash falls, ash flows and turbidite deposits. Smaller areas of dark gray mudstones interbedded with debris flows grouped together at the Porth Llauog Formation occurs around the margins of the rhyolite. Part of the southern margin of the inlet of Aber Mawr is formed by the mudstones and sandstones of the Trwyn Llundain Formation, from the Solva Group of Cambrian Rocks.  
The waters around the island have significant tidal effects , and tidal waterfalls occur between The Bitches .      The asymmetrical underwater flow can be 3.8 m / s (12.5 ft / s) northward (flood) and 1.9 m / s (6.2 ft / s) southward (ebb) , with some turbulence. The sound reaches some 66 meters (217 feet) deep, though a tidal island called Rock Horse protrudes from the water at low tide. 
A 400 kW tidal power turbine project was planned from 2014      and the first turbine was installed in December 2015. 
Owned and managed by the Royal Society for the Protection of Birds (RSPB),  the island HAS spectacular bird cliffs , coastal scenery and heathland . It is one of the best sites in Wales to see choughs , which are attracted by an ample supply of dung beetles .
Other common species include ravens , common buzzards , peregrines , northern wheatears , gulls , auks , manx shearwaters , razorbills and guillemots .
Ramsey has the most important gray seal breeding colony in southern Britain, with over 400 seal pups born each autumn.  In October 2017 the remnant storm of Ophelia hurricane was responsible for some 90 seal pup deaths. 
With a permanent population of just two human residents, the Royal Society for the Protection of Birds (RSPB) Warden and Assistant Warden who lives in a farmhouse there, the island is otherwise uninhabited. Tourist boats sail around the island and has ferry services run by Thousand Islands Expeditions Operates from Easter-31 October from St Justinian ‘s RNLI lifeboat station on the mainland.
Ramsey Island is surrounded by smaller islands, islets and rock clusters, including:
- The Bitches tidal race
- The Bishops and Clerks group, including:
- Carreg Rhoson and Maen Rhoson
- Daufraich and Maen Daufraich
- Emsger Gold South Bishop (37 yards, 121 feet)
- Llechau-isaf and Llechau-uchaf
- North Bishop (44 meters, 144 feet)
- Meini Duon ( Black Rocks )
- The Bitches
- Ynys Bery (71 meters, 233 feet)
- Ynys Cantwr ( tidal island , 54 meters, 177 feet)
- Ynys Eilun and Yil Eilun Bridge
- Ynys Gwelltog ( Grassy Island , 56 meters, 184 feet)
- Jump up^ The Rough Guide to Wales, Rough Guides, Rough Guide Travel Guides, Mike Parker, Paul Whitfield, 4, Illustrated, Rough Guides, 2003,ISBN 1-84353-120-8,ISBN 978-1-84353-120- 3, pg. 194
- Jump up^ British Geological Survey in 1992 1: 50,000 scale geological map sheet 209 provisional (England and Wales)St David’s
- Jump up^ Howells, MF 2007British Regional Geology: Wales(Keyworth, Nottingham, British Geological Survey) pp 45-51
- Jump up^ “Nature”
- Jump up^ “The Bitches” . the-bitches.co.uk .
- Jump up^ -. “Bitches tidal rapid – South – Wales – Rivers – The UK Rivers Guidebook” . ukriversguidebook.co.uk .
- Jump up^ “Canoe Wales -” . canoewales.com .
- Jump up^ “Bitches and Tides”
- Jump up^ Evans, Paul Stephen (2014). Hydrodynamic characteristics of macrotidal straits and implications for tidal stream turbine deploymentpp. 107-109, 169. PhD Thesis,Cardiff University
- Jump up^ Macalister, Terry. “Tidal power firm to sell electricity to EDF Energy”The Guardian , 25 September 2014.
- Jump up^ , Ellie. “First full-scale tidal generator in Wales unveiled: Deltastream array to power 10,000 homes using ebb and flow of the ocean” Daily Mail , August 7, 2014.
- Jump up^ Chris Kelsey (17 June 2015). “DeltaStream tidal energy device further delayed as a company seeks new funding” . walesonline .
- Jump up^ “Talking Tidal Energy Ltd.” Talking Tides: Martin Murphy of Tidal Energy ” . tidalenergyltd.com .
- Jump up^ “Turbine design turns the tide for renewables” . eurekamagazine.co.uk .
- Jump up^ “Giant tidal turbine on Pembrokeshire” . BBC. December 14, 2015 . Retrieved 14 December 2015 .
- ^ Jump up to:a b Countryside Council for Wales, National Nature Reserves | Ramsey(retrieved 2011-10-28).
- Jump up^ “About 90 Ramsey Island seal pups lost to Storm Ophelia” . BBC News . October 18, 2017 . Retrieved 25 October 2017