See the ‘Maribyrnong Catchment’ page for a detailed description of the catchment.
This Report Card provides an overview of water quality in the Maribyrnong catchment from 1 July 2014 to 30 June 2015. 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 2014-15, water quality in the Maribyrnong catchment was ‘Fair’.
Summary Table: The table below shows the percentage of the Maribyrnong catchment that falls into each scoring category. See scoring method for more information.
Upper and lower Jacksons Creek catchment
Deep Creek and the mid-Jacksons Creek, tributaries of the mid-catchment
Medium density urban and suburban tributaries
Densely populated urban and industrial tributaries and the lower Maribyrnong River
The routine monitoring across 15 sites give us information for about 77 per cent of the catchment. Approximately 2 per cent of the catchment was not included due to incomplete data resulting from the drying of waterways in the catchment. The remaining 21 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 these annual index scores and indicators with the Maribyrnong’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.
Streams in the upper catchment, such as Riddells Creek, have little impact from urbanisation and industry, resulting in ‘Good’ water quality. The majority of the mid to upper catchment is primarily used for agriculture. Runoff from agricultural land can be a major source of sediment and nutrients in rural waterways, which lowers water quality. Due to lower rainfall reducing run-off over the 2014–15 period, these impacts were not as evident. An additional implication of reduced rainfall is the drying of smaller streams and a potential increase in salinity, as saline groundwater enters the waterways, as was seen in Deep Creek. It is likely to be what would naturally occur in some streams during times of low rainfall. Streams with areas of groundwater intrusion can retain isolated pools in otherwise dry streams and provide important habitat for some species such as Yarra Pygmy Perch during periods of drought.
Only 10 per cent of the land in the Maribyrnong catchment has been urbanised, which means that the overall water quality is generally better than in other more urbanised catchments. However, waterways in the lower catchment urban areas are impacted by the effects of pollution and stormwater associated with residential and industrial development. This is why water quality in highly-urbanised regions of the catchment rated ‘Very Poor’.
Smaller waterways flowing into the Maribyrnong River tended to show high levels of nutrients, low dissolved oxygen and low water clarity. This is primarily because they are small and the effects of pollution are more intense when there’s not much water to dilute it.
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, whilst heavy rainfalls can cause flooding and river bank erosion, and wash sediments, nutrients and pollutants into waterways.
Below average rainfall was observed in 2014–15. The BoM (2016) noted just two days during the year when significant rainfall (between 21–37 mm) was recorded.
Three environmental flows with a total of 629 million litres of water were released during February, May and June from Rosslynne Reservoir. These flows were not released to mimic “natural” river flows but to improve water quality in the lower Jacksons Creek and to maintain the habitat for the growing platypus population that inhabit the upper Jacksons Creek.
Environmental flows improve water quality and habitat for aquatic species, increase waterbird and wildlife numbers and improve the amenity of local waterways for people to enjoy.
Looking at the water quality scores for the Maribyrnong catchment going back to 2000, there is a trend of an overall improvement in water quality. During this time, water quality can be attributed to both climate and human activities.
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 and stream health.
During times of high rainfall and increased runoff, there is a decrease in water clarity and an increase in nutrients and pollutants resulting in poor water quality. The drought breaking rains in 2010 and the well above average rainfall in 2011 resulted in declines in water quality. Gradual water quality improvements under more average climatic conditions have occurred since then.
There appears to be no shift in the catchment water quality score from the previous assessment in 2013–14. At the sub-catchment level, water quality improvements occurred in Jacksons Creek and the Maribyrnong River upstream of the urban fringe, while declines occurred within the urban and industrial areas of Steele Creek and the lower Maribyrnong River.
Improvements in water quality have positive flow-on effects to the plants and animals that rely on waterways. Improvements to water quality and habitat restoration have ensured that the Jacksons Creek platypus colony is thriving.
The Government, authorities and community have implemented the following initiatives to improve waterway health in the Maribyrnong catchments:
Environment Protection Authority
A number of priority areas and actions have been identified in the Maribyrnong catchment to build on existing projects and initiatives. These include:
The following figures show a comparison of scores for each identified water quality indicator in the catchments and Port Phillip Bay.