Nepean River

Nepean River (Yandhai)
Cowpasture River, Mittagong River, London River
Major perennial river
Nepean River, Looking north towards Penrith, 2006
Name origin: In honour of Evan Nepean, in 1789
Country	Australia
State	New South Wales
Regions	Sydney Basin (IBRA), Southern Highlands, Macarthur, Greater Western Sydney
Municipalities	Wingecarribee, Wollondilly, Camden, Penrith, Hawkesbury
Part of	Hawkesbury-Nepean catchment
Tributaries
- left	Erskine Creek, Breakfast Creek (New South Wales), Warragamba River, Glenbrook Creek
- right	Burke River (New South Wales), Cordeaux River, Cataract River (Wollondilly)
City	Penrith
Source	Mittagong Range
- location	near Robertson
- elevation	766 m (2,513 ft)
Mouth	confluence with the Grose River to form the Hawkesbury River
- location	near Yarramundi
- elevation	2 m (7 ft)
Length	178 km (111 mi)
National park	Blue Mountains National Park
Reservoir	Lake Nepean

Nepean River (Aboriginal: Yandhai), is a major perennial river, located in the south-west and west of Sydney, New South Wales, Australia. The Nepean River and its associated mouth, the Hawkesbury River, virtually encircle the metropolitan region of Sydney.

The headwaters of the Nepean River rise near Robertson, about 100 kilometres (62 mi) south of Sydney and about 15 kilometres (9.3 mi) from the Tasman Sea. The river flows north in an unpopulated water catchment area into Nepean Dam, which supplies potable water for Sydney. North of the dam, the river forms the western edge of Sydney, flowing past the town of Camden and the city of Penrith, south of which flowing through the Nepean Gorge. Near Wallacia it is joined by the dammed Warragamba River; and north of Penrith, near Yarramundi, at its confluence with the Grose River, the Nepean becomes the Hawkesbury River.

The river supplies water to Sydney's 5 million people as well as supplying agricultural production. This, combined with increased pressures from land use change for urban development, means the river has been suffering significant stress.

There are eleven weirs located on the Nepean River that significantly regulate its natural flow. The river has been segmented into a series of weir lakes rather than a freely flowing river and is also impacted by dams in the Upper Nepean catchment.