The Blue Mountains National Park is a protected national park that is located in the Blue Mountains region of New South Wales, in eastern Australia. The 267,954-hectare (662,130-acre) national park is situated approximately 80 kilometres (50 mi) west of the Sydney CBD, and the park boundary is quite irregular as it is broken up by roads, urban areas and areas of private property. Despite the name mountains, the area is an uplifted plateau, dissected by a number of larger rivers. The highest point in the park is Mount Werong at 1,215 metres (3,986 ft) above sea level; while the low point is on the Nepean River at 20 metres (66 ft) above sea level as it leaves the park.

The Nepean River, is a major perennial river, located in the south-west and west of Sydney, New South Wales, Australia. The Nepean River, and, continuing by its downstream name, the Hawkesbury River, almost encircles the metropolitan region of Sydney.