Lake Illawarra

Our water quality monitoring program has shown Lake Illawarra to have good water quality. Find out more about the estuary and its unique features.

Lake Illawarra is located on the south coast of New South Wales near Wollongong. It is classed as a large lake positioned between the Illawarra Escarpment and the sea. The entrances has training walls to ensure the lake remains open to the sea.

Lake Illawarra is valued by local communities for its social, economic and recreational value. This large estuary supports significant tourism and commercial fishing industries, and provides for a wide range of recreational activities.

Estuary health and features

Water quality

As part of our water quality monitoring program we assess the water quality and ecosystem health of an estuary using a range of relevant indicators. We sample a subset of the estuaries between Wollongong and the Victorian border every 3 years. The most recent sampling in Lake Illawarra was completed over the 2021–22 summer when 2 sites were sampled on a monthly basis.

Lake Illawarra water quality report card for algae and water clarity showing colour-coded ratings (red, orange, yellow, light green and dark green, which represent very poor, poor, fair, good and excellent, respectively). Algae is rated 'excellent' and water clarity is rated 'good' giving an overall rating of 'good' or 'B'.

This report card represents 2 water quality indicators that we routinely measure: the amount of algae present and water clarity. Low levels of these 2 indicators equate with good water quality.

The report card shows the condition of the estuary was good with:

  • algae abundance graded excellent (A)
  • water clarity graded good (B)
  • overall estuary health graded good (B).

Find out more about our estuary report cards and what each grade means. Read our sampling, data analysis and reporting protocols and find out how we calculate these grades.

We have monitored water quality in Lake Illawarra since 2007. This table shows the water quality grades for this estuary over that time.

Lake Illawarra historic water quality grades from 2007-08 for algae and water clarity. Colour-coded ratings (red, orange, yellow, light green and dark green represent very poor (E), poor (D), fair (C), good (B) and excellent (A), respectively).

Grades for algae, water clarity and overall are represented as:

  • A – excellent
  • B – good
  • C – fair
  • D – poor
  • E – very poor.

As part of our Beachwatch program we assess swimming suitability at 1 swimming site in Lake Illawarra using microbial indicators. Shoalhaven City Council collect samples at each site weekly between December and February to calculate the suitability grade. Sampling is ongoing. The grade reflects the most recent 56 water quality results to February 2022. Find out more about how we monitor beach water quality.

Local government area Swim site name Grade
Shellharbour Entrance Lagoon Beach Good

Estuarine, lake and lagoon water can sometimes be unsuitable for swimming, especially after rainfall when stormwater and wastewater can overflow into swimming areas. Learn more about what the grades mean and how we grade swimming sites on our beach classification webpage.

Water sampling and laboratory analysis was funded by Wollongong City Council and Shellharbour City Council.

Physical characteristics

Estuary type: Lake

Latitude (ºS) –34.54
Longitude (ºE) 150.88
Catchment area (km2) 238.4
Estuary area (km2) 35.8
Estuary volume (ML) 74,275.1
Average depth (m) 2.1

Tidal prism

Tidal prism data is available for this estuary. This tidal prism was measured in 2008.

Tide state Flow
(106 m3)
Local tidal
range (m)
Sydney Harbour
tidal range (m)
Ebb flow 2.14 0.66 1.32
Flood flow 2.7 0.63 1.32
Notes: km2 = square kilometres; m = metres; m3 = cubic metres; ML = megalitres.

Water depth and survey data

Bathymetric and coastal topography data for this estuary are available in our data portal.

Land use

Lake Illawarra estuary is surrounded by urban areas, particularly along the north- and south-eastern shorelines. This includes the townships of Berkeley, Lake Heights, Kanahooka, Oak Flats and Mount Warrigal. Urban areas currently comprise 20% of the catchment. This is likely to increase with extensive urban development planned for the western side of Lake Illawarra.

Grazing is the dominant land use in the catchment at 35%. Large areas of forest (25%) remain along the escarpment at the western boundary making up about 25% of the catchment.

National and marine parks

Community involvement

  • Landcare Illawarra support volunteer groups working to improve the environment in this region.
  • There are over 60 bushcare groups in the Wollongong area. Bushcare volunteers help regenerate and care for local bushland.
Lake Illawarra