Lake Illawarra is a coastal lake located between the Illawarra escarpment and the Pacific Ocean on the NSW South Coast some 90 km south of Sydney. Water flowing into it is both fresh (from the escarpment) and salty (from the ocean tides). There are hills to the north, west and south of the lake and sand dunes to the east.

Lake Illawarra is a large estuary compared to others on the NSW coast. It is also unusual in that despite a surface area of 35 square kilometres, it has a maximum depth of only 3.5m with a significant area of the lake being less than 1m in depth. The lake has a relatively long and shallow entrance that is periodically blocked off. Due to the nature of the sea entrance, very little tidal variation occurs in the lake.

Lake Illawarra comes under the jurisdiction of both Wollongong & Shellharbour Councils - different areas for each. Other authorities managing the lake are Lake Illawarra Authority 02 4224 9600 and Waterways Authority 02 4227 3644.

Windang is a small residential & holiday town on the eastern shore of Lake Illawarra overseen by Wollongong Council.