Lake Illawarra is a semi-enclosed basin where fresh water from surrounding land mixes with sea water brought in by the tides. The resulting mix, known as brackish water, forms an aquatic habitat where environmental conditions are extremely variable.

Neither freshwater nor marine plants and animals find the lake to their ideal liking. Relatively few species are capable of coping with the constantly changing estuarine conditions. However the lake is highly productive and ecologically complex.

See also complete list of all species found in the lake

Acknowledgements: The Authority wishes to thank Iradj Yassini, Chris Chafer and the Illawarra Catchment Management Committee for their photos, information and assistance with this section.