Swimming conditions in this website are predicted from the likelihood of bacterial contamination at typical recreational sites based on correlations with salinity levels as a proxy for rainfall and pollutants runoff. Swimming sites could also be affected by harmful algae blooms which would not be informed through this website. For further information on the presence of harmful algae blooms visit Hornsby Water Quality or call Water NSW algae hotline 1800 999 457.
Pollution is likely  Swim at own risk Pollution is unlikely
(average last 24 hours, parts per 1000)
|Latest Data||Status||% 'Pollution unlikely'
in last 12 months
|Bar Island||30.8||23 Jun 06:15||96|
|Bennetts Bay||29.4||23 Jun 06:15||96|
|Brooklyn Baths||33.9||23 Jun 06:00||100|
|Calabash Bay||28||23 Jun 05:45||86|
|Courangra Point||25.8||23 Jun 06:15||99|
|Crosslands Reserve||15.9||23 Jun 06:15||17|
|Dangar Island||34.1||23 Jun 06:00||100|
|Deadhorse Bay||33.2||23 Jun 06:00||100|
|Gunyah Point||34.3||23 Jun 06:00||100|
|Laughtondale||13.5||23 Jun 06:30||99|
|Milsons Passage||32.3||23 Jun 06:15||100|
|Sandbrook Inlet||31.8||23 Jun 06:15||100|
|Twin Beaches||29.9||23 Jun 06:15||100|
Swimming conditions are predicted from the likelihood of bacterial contamination based on recorded salinity levels as a proxy for rainfall and pollutants runoff. The following steps are undertaken in the calculation of swimming conditions:
|Crosslands Reserve||Pollution is likely = Salinity is less than 20 ppt |
Swim at your own risk = Salinity between 20 and 22 ppt
Pollution is unlikely = Salinity is more than 22 ppt
|Courangra Point & Laughtondale||Thresholds are based on the historical 30th and 10th salinity percentiles|
|All other locations||Pollution is likely = Salinity is less than 21 ppt |
Swim at your own risk = Salinity between 21 and 24 ppt
Pollution is unlikely = Salinity is more than 24 ppt
The above thresholds have been calculated based on Hornsby Shire Council's water quality monitoring program and the 2018 National Health and Medical Research Council Guidelines for Managing Risks in Recreational Water. These thresholds take into consideration the NHMRC categories based on the 95th percentile for Enterococci and the salinity values being monitored from Council’s on-site water quality monitoring station. These thresholds will change as more bacteria data comes available in particular after wet weather sampling. The occurrence of freshwater in the estuary following rainfall increases the likelihood of pollution being present. Obvious signs of stormwater pollution are water discoloration as well as debris in the water and tide line. When pollution is likely, swimmers may be at increased risk of contracting illness and swimming at these times should be avoided.
This system utilises recorded data captured by Manly Hydraulics Laboratory (MHL) on behalf of Hornsby Shire Council. Recorded data is download at 7 am each morning at all monitoring locations. Displayed salinity values are calculated as the average of salinity measurements for the latest 24 hours of data. At locations without recorded data, salinity is estimated using correlated values from nearby recorded data.
IMPORTANT: This information has been recovered directly from automatic recording equipment and has not been quality controlled by MHL. The State of NSW (of which MHL is an agency) does not warrant the quality, accuracy, currency, reliability or correctness of this information and accepts no liability for any loss, injury (including death), or damage which any person relying on this information may suffer.