The site was closed in 1998 for a $240 million upgrading, most of which is finished.

Mr Costa said the dam had been one of the most-visited tourist spots in Sydney and had attracted hundreds of thousands of people.

``We've invested in a major upgrade to the grounds surrounding the dam, including construction of new viewing platforms with sweeping views of the lake behind the dam wall,'' he said.

``The three new viewing platforms provide spectacular views of Lake Burragorang, as well as the dam itself.''

The new facilities include shade shelters, picnic tables, seating and toilets. More than 30 signs will be installed to tell visitors about the dam, its history and its catchment for drinking water.

Historical equipment used in the construction and operation of the dam has been placed around the grounds, which will be open from 8am to 5pm on weekdays and 8am to 6pm on weekends and public holidays during summer. After daylight saving ends the hours will be 8am to 5pm seven days a week.

A free shuttle bus will operate from Penrith station on weekends through November.