The reservoir's usable capacity is . Prior to April 2006, the usable capacity was , before the Deep Water Storage Recovery project was completed. There are fears, however, that population pressures may stretch the reservoir's ability to furnish Sydney residents with needed water well into the 21st century. The city's population is rising by about 50,000 every year. Water restrictions (limited usage purposes and times), were imposed late in 2003 and are reapplied during serious
droughts, which are expected to become more frequent. There have been times when the reservoir has become seriously depleted. On 8 February 2007 the lake recorded an all-time low of 32.5% of capacity, although by late 2008 the water level had returned to 60% of capacity. To reduce the likelihood of a water supply failure, the NSW Government authorised the construction and operation of the
Sydney Desalination Plant to augment Sydney's water supply. The dam reached maximum capacity and spilled in March 2012, the first time it had done so in fourteen years. This is consistent with increasingly
extreme weather events, where longer periods of drought and reduced total rainfall, is expected to be punctuated with shorter, heavier and more sporadic downfalls events. In November 2019, government proposed a $700 million plan to raise the height of the dam by 14 metres. The purpose is stated as providing flood mitigation for downstream land. Critics have alleged it may be to allow rezoning of prime agricultural in the flood zone, to residential property for commercial developers. Increasing the capacity would result in flooding large areas of native wildlife habitat, in a relatively protected water catchment area. It would also flood large areas of native vegetation, that provides a substantial
carbon dioxide sink, without proposal for replacement. The announcement was made while an application for concessions to extend mining operations inside the drinking water catchment areas, is under consideration. In the first week of December 2019, the water catchment area experienced
large bush fires, during a widespread and extreme fire season in Eastern Australia. ==Public access==