Water Quality


Boat detail

Hornsby Shire Council's water quality monitoring program has been operating since October 1994. Currently 60 sites are monitored across major catchment and land use types and at water reuse sites. At each site a range of physical, chemical and biological parameters are measured to ascertain the health of the waterway.

The following conclusions can be made to date:

  • Areas of highest water quality are associated with the least disturbed catchments.
  • Biological diversity varies according to the predominant land use. Communities at industrial and highly impacted urban sites are characterised by low species diversity, whereas rural sites have a higher species diversity.
  • Areas where the water quality is impacted or consistently degraded, receive impacts from either stormwater, high flows, periodic pollution incidents, sewer overflows or effluent discharges.
  • All urban and industrial areas contribute the highest concentrations of contamination via stormwater runoff. Concentrations of nutrients, suspended solids and faecal coliforms are significantly greater within these land use zones during wet weather.
  • Wet weather is problematic for sewage conveyance systems and treatment plants as indicated by the increased frequency of sewer overflows and number of bypass events during these periods.
  • The industrial areas at Thornleigh, Mount Kuring-gai and Hornsby continually have poor water quality with high concentrations of suspended solids, nitrogen and faecal coliforms.
  • Pollution of streams from on-site disposal or pumpout of effluent is evident within the rural areas.
  • Upgrades of West Hornsby and Hornsby Heights Sewerage Treatment Plants (STP's) have significantly reduced nitrogen levels entering the estuarine areas. Since about 2002, monitoring has indicated a reduction in nitrogen levels within the upper Berowra estuary with a reduced occurrence of algal blooms. Nevertheless, nitrogen and chlorophyll-a levels are still of concern.

The results obtained from this program are used to identify trends in water quality through time and to highlight the impacts of land use on the receiving waterways. Councils' Environment Division uses the information as a basis of assessing performance of stormwater quality improvement devices and water reuse projects. Use of this information within the Division is designed to identify impacts and existing catchment conditions, which enables Council to establish management objectives and strategic options for prioritised implementation and longer term monitoring of improvements in aquatic ecosystem health.

For further information please refer to:

Previous annual reports

For further information on water quality, please contact:

Elizabeth Bulley
Environmental Scientist - Water Quality Assets
Phone: (02) 9847 6965
Email: ebulley@hornsby.nsw.gov.au