Morecambe Bay is a large multiple estuary, not a bay as the name suggests, 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 . In 1974 the second largest gas field in the UK was discovered west of Blackpool, with original reserves of over 7 trillion cubic feet (tcf) (200 billion cubic metres). At its peak 15% of Britain's gas supply came from the bay but production is now in decline and the main field was mothballed in 2011.