Mundaring Weir is a concrete gravity dam (and historically the adjoining locality) located 39 kilometres (24 mi) from Perth, Western Australia in the Darling Scarp.

The weir leaks, and the photos below show consistent stain/moisture points between 2008, 2010, 2020 and 2024, where water moves through the structure: A new pump station with an initial capacity of 165,000 cubic metres (5,800,000 cu ft) per day, and an ultimate capacity of 240,000 cubic metres (8,500,000 cu ft) per day, commenced operations in March 2014.

It was only after the completion of the weir that the location became popular with picnickers and sightseers, as the project caught the imagination of the public in Perth.

There is also the Kookaburra outdoor cinema, and the Department of Environment and Conservation has the Hills Forest activity centre, as well as a regional administrative office.

Before rationalisation of its work force at this locality, the Water Authority of Western Australia's operations at the Weir maintained housing for its workers.

There is a youth hostel (built at the site of the now defunct primary school), an art gallery in the area, and many picnicking spots.

The 963 kilometres (598 mi) walking trail Bibbulmun Track commences in Kalamunda following Piesse Brook, then along the south side of the Helena valley.

Crossing the weir wall the track follows the northern side of C.Y.O'Connor lake before turning south and continuing the journey to Albany.