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Catchment water quality

Through its Rivers and Estuaries Science program, the Department of Biodiversity, Conservation and Attractions (DBCA) conducts fortnightly monitoring at 33 sites within 27 of the 31 sub-catchments of the Swan Canning river system. Data from this monitoring program is reported in a number of formats including annual catchment data reports and sub-catchment nutrient reports.

Catchment water quality data reports

Water quality data collected fortnightly from 33 catchment sites as part of the Swan Canning Water Quality Monitoring project is summarised into annual reports, which are available for download at the bottom of this page. 

Annual reporting against catchment targets

DBCA's key performance indicators of water quality for the catchment of the Swan Canning Estuary are:

  • total nitrogen and total phosphorus concentrations in 15 priority sub-catchments

Targets for catchments

Median total nitrogen and total phosphorus targets have been developed for catchment tributaries of the Swan Canning river system. In recognition of the long timeframes required for catchment management to affect nutrient levels in tributaries, both short term and long-term targets have been developed.  The long-term targets are based on Australian and New Zealand Environment and Conservation Council (ANZECC) (2000) trigger values for near pristine rivers while the short-term targets are double the ANZECC recommendations.

Target Total nitrogen (mgL-1) target Total phosphorus (mgL-1) target
Short-term 2.0 0.2
Long-term 1.0 0.1

Long-term (over 25-40 years) load reduction targets for nitrogen and phosphorus have been established through the Swan Canning Water Quality Improvement Plan. Although performance against these nutrient load reduction targets is not reported on annually, sub-catchment nutrient reports are available each year to provide information on nutrient loads from monitored sub-catchments. The nutrient load reduction targets guide long-term investment to improve water quality in those catchments contributing the greatest loads of nutrients to the river system.

Sub-catchment nutrient reports

Data that is collected fortnightly as part of the catchment water quality monitoring program is used to determine the nutrient concentrations and loads entering the Swan Canning Estuary. Long-term trends in this nutrient data are calculated every five years. However, calculations of total nitrogen (TN) and total phosphorus (TP) loads are used to report annually against catchment nutrient targets.

Five-yearly reporting

Nutrient data collected from 15 priority sub-catchments is compiled into 'catchment nutrient reports', which are produced every five years. In these reports, long-term (since 1999) trends in total nitrogen (TN) and total phosphorus (TP) concentrations are calculated and used to evaluate the effectiveness of management actions.

Annual update

The annual re-calculation of nutrient trends for each catchment is not appropriate due to the high inter-annual variability in nutrient concentrations/loads (which are very dependent on rainfall patterns). However, reporting of annual nutrient concentrations and loads from each catchment are calculated each year to track progress against targets. As a result, the front page of each five-year catchment report is updated annually to provide a catchment-by-catchment measure of annual TN and TP concentrations and loads entering the Swan Canning Estuary.

The five-yearly and annual nutrient reports for each sub-catchment are available below.