Dulas Bay (Welsh: Bae Dulas) is a small bay on the north east coast of Anglesey (Ynys Môn), north Wales, forming the boundary between Llaneilian and Moelfre communities. The bay is bordered by three beaches. Overview The north-western beach is the sand/shingle/mud estuary Traeth Dulas (Dulas Beach); southeast of this is the tiny Traeth Bach (Small Beach) and the sandy Traeth yr Ora (Beach of The Fortified Landing Place). The estuary running through Traeth Dulas is that of the Afon Goch (Red River). The Traeth Bach and Traeth Yr Ora at high tide are separated by a rock outcrop called Craig y Sais (The Saxon Rock). At low tide, however, it is possible to walk on the sand between the three beaches and also onto the beaches of Lligwy Bay to the south. Traeth Dulas is most affected by the tide, so much so that the most inland parts of the estuary are salt marshes. A walk is the circuit starting at Lligwy Bay, taking in Traeth Ora, the Pilot boat Pub and an option to reach the top of nearby Mynydd Bodafon. About a mile and a half off shore is a small island, Ynys Dulas, which is roughly 620m long and has a maximum width of 205m. It is known for the seals which live on the island (hence it is also known locally as Seal Island), but it is too small for human habitation. However, upon this island is a round structure with a cone-shaped top that was built in 1821 by James Hughes to store food and provide shelter for shipwrecked seamen. Two much smaller islands, Garreg Allan (The Outer, Expelled or Furthest Stone, not visible by the naked eye from the shore, behind Ynys Dulas) and Ynys y Carcharorion (Prisoners' Island, nearer Traeth Dulas) are also present. Oil tankers can often be seen out some miles from shore in the Irish Sea, as they wait for the tide to enter the River Mersey for discharge at Tranmere Oil Terminal. Bathymetry and history The bathymetry of the bay is interesting. No water less than a mile out is over twenty metres deep. The most steep decline in the sea bed is found out from Traeth yr Ora. Conversely, a raised shelf of seabed about 1.5 km long reaches out just beyond Garreg Allen, none of which is over 5 metres deep. This is followed by a