Swimming Conditions
Description
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. Avoid water that is discoloured, murky or smells unpleasant when considering going for a swim. 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 unlikely, enjoy your swim!
Pollution is possible, take care
Pollution is likely, avoid swimming today
Station outage
| Location | Water Temperature |
Salinity |
Latest Data | Status |
|---|---|---|---|---|
| (average last 24 hours) [˚C] | (average last 24 hours) [parts per 1000] | |||
| Bar Island | 26.0 | 27 | 28 Nov 22:00 | |
| Bennetts Bay | 26.0 | 26.5 | 28 Nov 22:00 | |
| Brooklyn Baths | 23.1 | 33.6 | 28 Nov 22:00 | |
| Calabash Bay | 150.0 | 150 | 28 Nov 22:00 | |
| Courangra Point | 25.8 | 22.5 | 28 Nov 22:00 | |
| Crosslands Reserve | 27.8 | 14.8 | 28 Nov 17:00 | |
| Dangar Island | 23.1 | 33.8 | 28 Nov 22:00 | |
| Deadhorse Bay | 23.1 | 32.9 | 28 Nov 22:00 | |
| Gunyah Point | 23.1 | 33.9 | 28 Nov 22:00 | |
| Wisemans Ferry | 26.2 | 7.5 | 28 Nov 22:15 | |
| Milsons Passage | 26.0 | 30.1 | 28 Nov 22:00 | |
| Sandbrook Inlet | 26.0 | 29.1 | 28 Nov 22:00 | |
| Twin Beaches | 26.0 | 27 | 28 Nov 22:00 | |
Overview of Swimming Conditions Calculations
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:
- Salinity data is collected every 15 min in the lower estuary using seven real-time monitoring stations. Recorded data is download at 7 am each morning at all monitoring stations.
- At locations without recorded data, salinity is estimated using correlated values from nearby recorded data. Water temperature from nearby stations is also shown.
- The latest salinity is calculated at each location as the average of the last 24 hours.
- The latest salinity is compared to different thresholds depending on the location to determine a given swimming condition. Thresholds for each location are shown in the table below.
| Location | Thresholds |
|---|---|
| Crosslands Reserve | Pollution is unlikely, enjoy your swim! = Salinity is more than 18 ppt Pollution is possible, take care = Salinity between 12 and 18 ppt Pollution is likely, avoid swimming today = Salinity is less than or equal to 12 ppt |
| Courangra Point & Wisemans Ferry | Thresholds are based on the historical 30th and 10th salinity percentiles |
| All other locations | Pollution is unlikely, enjoy your swim! = Salinity is more than 24 ppt Pollution is possible, take care = Salinity between 21 and 24 ppt Pollution is likely, avoid swimming today = Salinity is less than 21 ppt |
Thresholds for Swimming Conditions Calculations
The 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.