• As an island, Ireland, which comprises both the Republic of Ireland and part of the United Kingdom, is surrounded by water on all sides. For geographical and cartographical (map-making) purposes, the Earth's hydrosphere--all liquid water covering the planet's surface--is divided into units such as oceans, seas and lakes. Five such units--one ocean, two seas and two straits--make up the bodies of water that surround Ireland.
  
  

Atlantic Ocean

• The Atlantic Ocean is the largest body of water surrounding Ireland. Second largest of the world's five oceans (after the Pacific), the Atlantic divides the continents of Europe and Africa on one side from North and South America on the other. With a total area of approximately 76,762,000 square kilometers, the Atlantic covers more than 20 percent of the planet's surface. The Atlantic derives its name from the Greek mythological figure, Atlas.
  
  

Irish Sea

• Another body of water surrounding Ireland is the Irish Sea. This sea connects to the Atlantic Ocean at its northern and southern points via the North and Saint George's Channels. To the west and east lie the Republic of Ireland and all four constituent countries of the United Kingdom (England, Scotland, Ireland and Wales). Several islands can be found in the Irish Sea, the largest of which are the Isles of Man and Anglesey. Historically, the Irish Sea has played a significant role in trade and later tourism between Ireland and Britain.
  
  

Celtic Sea

• Located to the immediate south of Ireland, the Celtic Sea is bounded by the Atlantic Ocean on the west and south, and the St. George's, Bristol and English Channels to the east. The sea also connects with the coastlines of England, Wales and France. English naturalist E.W.L. Holt gave the Celtic Sea its name in 1921. "Celtic" refers to the cultures of the region that would later evolve into the Irish, Scottish and Welsh ethnic identities. The term was not widely adopted for several decades.
  
  

North Channel and St. George's Channel

• The smallest bodies of water surrounding Ireland are the North and St. George's Channels. Both channels are naturally occurring straits (narrow bodies of water separating two landmasses). The North Channel is the narrower of the two, and has historically served as a key route for trade and travel between the regions now known as Scotland and Northern Ireland. The North Channel should not be confused with an identically named strait located adjacent to the Canadian province of Ontario.