Prospect Reservoir, Water reservoir in Prospect, Australia.

Prospect Reservoir is a 50,200-megalitre potable water storage reservoir formed by the Prospect Dam across Prospect Creek in the Western Sydney suburb of Prospect, New South Wales. The zoned earth embankment dam is 26 m high and about 2.2 km long, the first earthfill embankment dam in Australia. The water body has an irregular shoreline with wooded peninsulas and an island, bordered by dark green tree cover, an open grassy strip and a cleared brownish area at the southern end.

The dam was completed in 1888 as part of the Upper Nepean Scheme, an engineering effort to bring water from the highlands south of Sydney into the growing city. It is now listed on the New South Wales State Heritage Register, recognized as a key piece of colonial-era infrastructure.

The land around the reservoir is one of the last places in Western Sydney where the woodland of the Cumberland Plain survives in a recognizable form, nearly cleared everywhere else. Visitors walking the eastern trails can see native plants and hear birds that have become rare in the surrounding suburbs.

The visitor area on the eastern side is reached via William Lawson Drive, where parking and picnic facilities are available near the water. The walking tracks through the nature reserve are generally easy to follow, though sturdy footwear helps on the unpaved sections after rain.

Although the reservoir is still an active part of Sydney's water supply, the water itself is off-limits to the public, so the lake can only be seen from the shore. This restriction has kept the water's edge largely undisturbed, which is part of why wildlife is so visible along the banks.