Water Quality

Hornsby Shire Council has had some major successes in water quality improvement and conservation.

How is the health of waterways monitored?

Hornsby Shire Council carries out a comprehensive water quality monitoring program, with staff regularly collecting and testing samples from more than 60 locations.There are also six real-time monitoring stations along the estuary gradient which collect data every 15 minutes and transmit to a web portal every 6 hours. This web portal provides information on current water quality, estuarine health and swimming conditions.

View the latest data on the Web Portal

Algal Bloom Monitoring

There are currently no algal blooms detected in Hornsby Shire waterways.

Alerts will be posted on this web page and on Council's Facebook page in the event of an algal bloom occurrence.

To find out what to do when a harmful algal bloom is present click in either of the following links:

What is the water tested for?

The water is tested to assess long-term ecosystem health, stormwater harvesting programs and activities that influence water quality such as wastewater treatment plants.

At each site a portable probe (YeokalTM 615 Sonde) is used to measure:

  • Dissolved Oxygen (DO% sat and DO mg/L)
  • Electrical Conductivity (EC ms/cm and ECµs/cm)
  • pH
  • Salinity (ppt)
  • Temperature (ºC)
  • Turbidity (NTU)

A sample is also collected from each site and tested for:

  • Bacteria (Faecal coliforms (CFU/100mL),Ecoli and/or Enterococci (CFU/100mL)
  • Nutrients (total nitrogen, oxidised nitrogen,ammonia nitrogen and total phosphorus) (mg/L)
  • Suspended Solids (mg/L)
  • Chlorophyll-a (µg/L) at estuarine sites only


The general trend is that better water quality results are recorded where catchments remain primarily undisturbed, usually in National Parks and Nature Reserves. Results tend to decline downstream of rural and urban settlements, with the most impacted water quality being recorded downstream of industrial areas. Stormwater and sewage from overflows or failing infrastructure continue to be a problem in industrial and urban catchments. Onsite wastewater management systems continue to place stress on waterways in rural settlements. Rural catchment activities such as the intensive use of fertilisers and reduced vegetation also impact receiving waters further downstream.

Estuarine areas are generally good, though the upper sections of Marramarra and Berowra Creeks show signs of impacts from the upper catchments. Despite significant upgrades to the West Hornsby and Hornsby Heights Sewage Treatment Plants in early 2000, both Berowra Creek and Calna Creek are impacted by treated effluent being discharged.

Rainfall has a major impact on water quality and can influence water quality by increasing turbidity and suspended solids in stormwater, washing rubbish and contaminants into streams and creeks and increasing the likelihood of overflows from sewerage systems into waterways in developed areas. The magnitude of contamination at a sampling site is related to the quantity and the intensity of rainfall and to how recently rainfall occurred before the sampling.