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 310 km² (120 sq mi). In 1974 the second largest gas field in the UK was discovered 25 miles (40 km) west of Blackpool, with original reserves of over 7 trillion cubic feet (tcf) (200 billion cubic metres).