Morecambe Bay is a large bay in northwest England, nearly due east of the Isle of Man and just to the south of the Lake District National Park. It is the largest expanse of intertidal mudflats and sand in the United Kingdom, covering a total area of 310 km².

The rivers Leven, Kent, Keer, Lune and Wyre drain into the Bay, with their various estuaries making a number of peninsulas within the bay, such as Humphrey Head.

Much of the land around the bay is reclaimed, forming saltmarshes used in agriculture. Morecambe Bay is also an important wildlife site, with abundant bird life and varied marine habitats, and there is a bird observatory at Walney Island.

The bay is also notorious for its quicksand and fast moving tides (it is said that the tide can come in "as fast as a horse can run"). It is particularly infamous due to the '2004 Morecambe Bay Disaster' in which 21 Chinese illegal immigrant cockle pickers drowned due to the tide.

There have been royally appointed local guides (holding the post of Queen's Guide to the Sands) for crossing the bay for centuries. This difficulty of crossing the bay added to the isolation of the land to its north which, due to the presence of the mountains of the Lake District, could only be reached by crossing these sands or by ferry, until the Furness Railway was built in 1857. This skirts the edge of the bay, crossing the various estuaries.