Morecambe Bay, bay of the Irish Sea deeply indenting the northwest coast of England between the port of Barrow-in-Furness to the north and the seaside resorts of Morecambe and Heysham to the south. The bay separates the Furness region of the historic county of Lancashire (now in the administrative county of Cumbria) from the remainder of Lancashire. Much of the Lake District massif, lying to the north, drains into the bay.