The bay is approximately 10 km in width at its north-south base and 7 km in length to its apex at the centre of the city of Dublin, stretching from Howth Head in the north to Dalkey Point (at Dún Laoghaire) in the south. The artificially created Bull Island (North Bull Island) is situated in the northwest corner of the bay and features a 5km long sandy beach, Dollymount Strand, fronting an internationally recognised wildfowl reserve.
It is the expanse of the Irish Sea into which the River Liffey and the River Dodder flow after their conjunction at Dublin (from the Irish "Dubh Linn" meaning "Black Pool"), as well as the River Tolka and various smaller rivers.
The metropolitan area of the city of Dublin almost completely surrounds three sides of the bay (the north, west, and south), while the Irish Sea lies to the east. Also called Baile Átha Cliath (meaning "Ford of the wattles"), Dublin was founded by the Danes at the point where they were able to ford the River Liffey with the first wattle bridge up from the estuary. As technology moved forward in Ireland it became possible to bridge the rivers further and further down to the sea, and to reclaim the swampy foreshore. The city spread from its birthplace around Guinnesses and James's Gate, to the sea and out along the coastline north-east towards Howth and south-east towards Dalkey.
James Joyce set practically all the action of his novel Ulysses around the bay from the Forty Foot in which Buck Mulligan washed in the morning of Bloomsday to Howth, where Mr Bloom made love to his Molly under the rhododendrons.
Dublin Bay, being rather shallow and having many sandbanks and rocky outcrops, was notorious for shipwrecks; especially when the wind was from the east. Up until modern times many ships and their passengers were lost along the treacherous coastlines out from Howth and Dun Laoghaire, not a kilometer from shore.
Over 500 crew and passengers (the majority military personnel) were lost when the steamship RMS Leinster was torpedoed and sunk by German U-Boat UB-123 on 10 October 1918. She lies in 33 meters (108 ft) of water at latitude 53° 18' 88" N (53.324); longitude 5° 47' 71" W. (-6.803)
In 1972 the Dublin Port and Docks Board proposed the building of an oil refinery in Dublin Bay. The plan was vigorously opposed by environmentalists, including Dublin City Councillor Seán D. Loftus, on the grounds that it posed a serious risk of pollution. Loftus, a life-long campaigner for Dublin Bay, changed his name by deed poll to "Seán Dublin Bay Loftus" when standing for election to the Dáil. Although he was not elected, he succeeded in highlighting the issue and the proposal was eventually turned down by the Minister for Local Government, James Tully (Loftus later changed his name by deed poll to "Seán Dublin Bay Rockall Loftus" as part of a campaign to press the Irish Government to make a territorial claim to the Rockall islet off the coast of County Donegal). Loftus has also led opposition to the 2002 application by the Dublin Port Company to fill in 52 acres of Dublin Bay. Other suggestions for the bay have included a proposal to build giant underwater gas storage tanks, and to infill the near-lagoon behind North Bull Island to form a leisure park.