Lake Illawarra (Aboriginal Tharawal language: various adaptions of Elouera, Eloura, or Allowrie; Illa, Wurra, or Warra meaning pleasant place near the sea, or, high place near the sea, or, white clay mountain[1]) is an open and trained intermediate wave dominated barrier estuary[3] or large coastal lagoon ,[1] is located in the Illawarra region of New South Wales, situated about 100 kilometres (62 mi) south of Sydney, Australia.

Located south of the city of Wollongong, north of the city of Shellharbour, and 5 kilometres (3.1 mi) northeast of Dapto, Lake Illawarra receives runoff from the Illawarra escarpment through Macquarie Rivulet and Mullet Creek, drawing from a catchment area of 238 square kilometres (92 sq mi).

With an average depth of 2.1 metres (6 ft 11 in), the relatively shallow lake, brought about because of infilling by sand which has been eroded from the surrounding catchments,[6] covers a surface area of 35.8 square kilometres (13.8 sq mi).

Located on the western shore of Lake Illawarra at Yallah is the natural gas-powered Tallawarra Power Station.

On 12 January 2009, it was suspected a man was bitten by a bull shark whilst snorkelling at Windang, near the mouth of Lake Illawarra.