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Water levels and algal testing for Lake Cathie

NSW Health is responsible for the management of Lake Cathie-Lake Innes water quality from a health perspective. NSW Health are the entity that make a decision on whether the water is safe for swimming.

NSW Fisheries are responsible for managing the water quality in relation to fishing. 

Council undertakes water quality and algal testing to provide advice from an amenity perspective.  For example if the water is dirty, or if there is odour as it relates to people using the adjoining recreation areas. We undertake this testing and provide advice and signage as part of our role in managing the land surrounding the Lake which includes the public reserve, related infrastructure and play areas. We perform this testing via our laboratory fortnightly. Water quality results are available in the table below.

In addition, Council monitors the water levels twice a day for the purpose of protecting public infrastructure and property in circumstances relating to possible flood impacts.

Is it safe to swim?

If you have concerns about the quality of the water and want to find out if it is safe to swim, please contact NSW Health, or NSW Fisheries to seek the relevant advice. It's important to be aware that during dryer than usual times low water levels or brown water which may be seen does not necessarily mean the Lake is dying or is unsafe for recreational users. However if you have concerns we encourage you to contact the North Coast Public Health Unit on 02 6588 2750. 

Water levels

The NSW Government uses automatic equipment to track Lake Cathie water levels. There are two different height datum’s used when referencing the lake level and the tidal level.  The lake levels, and those reflected on the Manly Hydraulics (MHL) site (the monitoring undertaken for NSW Government) are recorded against the Australian Height Datum (AHD). This datum point is commonly used to measure land levels but is also used to record water levels. AHD is based on mean sea level (i.e. the middle of the tidal range) and so 0.0m AHD is Mean Sea Level.

The ocean tide levels are recorded against a different datum, which is established on the Lowest Astronomical Tide (LAT). The difference between the lake level recorded on the Manly Hydraulics site and the corresponding ocean level commonly referenced in “tidal charts” is easily explained by the difference between these two datum’s. For reference, 0.0m LAT is actually 0.9m lower than AHD.

Follow the water level information here noting results are in AHD datum:  Manly Hydraulics Water Level Reporting

Water quality and algal levels

For algal alerts and pollution incidents refer to the Related Information tab on this page.

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This page was last updated on: 12 June 2020