High Quality Content by WIKIPEDIA articles! Belfast Lough (Irish: Loch Lao or Loch Laoigh; Ulster-Scots: Bilfawst Loch) is a large, natural intertidal sea lough at the mouth of the River Lagan on the east coast of Northern Ireland. The inner part of the lough comprises a series of mudflats and lagoons. The outer lough is restricted to mainly rocky shores with some small sandy bays. Belfast Lough is the gateway for Belfast to the Irish Sea.