See the ‘Werribee Catchment’ page for a detailed description of the catchment.
This Report Card provides an overview of water quality in the Werribee catchment from 1 July 2015 to 30 June 2016. The quality of the water is given an overall score by combining the results of six standard water quality parameters: nutrients, water clarity (turbidity), dissolved oxygen, salinity (conductivity), pH (acidity/alkalinity) and metals.
In 2015–16 the water quality in the Werribee catchment was ‘Poor’.
Summary Table: The table below shows the percentage of the Werribee catchment that falls into each scoring category. See scoring method for more information.
The Werribee River and rural areas in the upper and mid-catchment
Small creeks in rural areas and the lower catchment
Smaller creeks that drain industrial areas in the lower catchment
The routine monitoring across 13 sites provides information for about 45 per cent of the catchment. Approximately 28 per cent of the catchment was not included due to incomplete data, which resulted from the drying of waterways in the catchment or unsafe site access. The remaining 27 per cent of unmonitored catchment is mostly rural, which would typically score as ‘Fair’ for this region.
See the Monitoring Programs page for changes to the monitoring program.
The section 'Changes over time’ compares this year’s annual index scores and indicators with Werribee’s scores from previous Report Cards (since 2000). Results can also be compared to other catchments.
Site-specific details about parameters can be accessed via the map.
The water quality in the Werribee catchment is ‘Poor’. There is a clear pattern throughout the Werribee catchment, with water quality scores reflecting the impacts of climate and various land uses.
As a consequence of continued low rainfall from 2014–15 into 2015–16, water quality in the catchment has continued to decline. Several sites in the upper Werribee, which historically display ‘Good’ to ‘Very Good’ water quality, dried up during the year, resulting in their exclusion from the assessment. The exclusion is based on the lack of data from these sites and it is expected that the return of water to these streams will result in an improvement to the catchment’s overall rating.
The different land uses within the Werribee catchment largely explain the changes in water quality. In the upper Werribee catchment, the near natural areas in the Lerderderg State Park usually have ‘Good’ to ‘Very Good’ water quality due to minimal human impact, while the rural streams in the upper and middle catchment typically score ‘Fair’. In rural locations, streams flowing through farm land have often been heavily cleared of vegetation which means that sediment and nutrient runoff can enter the waterways. Additionally, nutrients can enter waterways from livestock damaging creeks and river banks, and through discharges from septic tanks.
As the waterways of the Werribee catchment flow into the more populated and industrial regions of the lower catchment, water quality declines further. This is mostly due to large volumes of stormwater draining off hard surfaces into waterways when it rains, carrying sediment and other pollutants (such as metals) into waterways from roads, industrial, and intensive agriculture areas. The water quality in these areas is generally ‘Poor’ to ‘Very Poor’.
During 2015–16 water quality improved slightly in the heavily urbanised waterways of Kororoit and Skeleton Creek due to reduced stormwater inputs.
Short-lived environmental and extreme weather events can impact water quality in waterways. Long-term dry spells can result in reduced river flows, increases in salinity and algal blooms, while heavy rainfalls can cause flooding and river bank erosion, and can wash sediments, nutrients and pollutants into waterways.
Below average rainfall was observed in 2015–16. The Bureau of Meteorology (2016) noted just two events when significant rainfall (22–24 mm) was recorded.
In January a blue-green algae bloom developed in the Werribee River, downstream of the Maltby Bypass and persisted for several weeks. Heavy rainfall in late January, combined with an environmental water release, dissipated the bloom. The algal bloom returned in early March, but dissipated with the aid of an additional environmental water release.
Five environmental flows with a total of 618 million litres of water were released. Three releases were from Merrimu Reservoir into Pyrites Creek but these did not continue to flow downstream from Melton Reservoir. One of these releases provided several months of baseflow to provide habitat for aquatic species as natural river flow was absent due to the dry conditions. The other two releases were to improve habitat for aquatic species by scouring sediments. Two releases from Melton Reservoir were to improve water quality in the lower reaches of the Werribee River.
Environmental flows improve water quality and habitat for aquatic species, boost recreational fishing, increase waterbird and wildlife numbers and improve the amenity of local waterways for people to enjoy.
Water quality scores for the Werribee catchment from 2000 to present, show a trend of improvement in water quality, despite declines in water quality over the last two years. During this time, changes in water quality can be attributed to both human activities and the climate.
During times of low rainfall, stream condition may appear to be good as there are little or no inputs from runoff, resulting in lower levels of nutrients and pollutants and improved water clarity. However, reduced water levels and dissolved oxygen levels, at these times can decrease overall water quality. In its “natural” state the streams of the Werribee catchment would regularly dry during low rainfall years leaving remnant pools were ground water meets the surface.
More sustained river flows occurred after the drought broke in 2009–10, continuing into 2010–11. This resulted in an increase in nutrients and pollutants entering the waterways, which slightly reduced the water quality. Gradual water quality improvements under average climatic conditions occurred up to 2013–14.
2014–15 saw the onset of dry conditions, the drying out of the Werribee catchment and a subsequent decline in water quality. Dry conditions continued throughout 2015–16, which resulted in further declines in water quality. Several waterways were reduced to isolated pools, while others dried up completely resulting in their exclusion from the assessment. It is expected the return of water to these streams will result in an improved catchment WQI score.
Government agencies, local councils and the community have implemented the following initiatives to improve waterway health in the Werribee catchment:
Environment Protection Authority (EPA)
For more information on projects and works in the Werribee catchment please see the Waterways Local Updates.
A number of priority areas and actions have been identified in the Werribee catchment that will build on existing projects and initiatives. Future priority management actions include:
The following figures show a comparison of scores for each identified water quality indicator in the catchments and Port Phillip Bay.