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 2013 to 30 June 2014. 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.
Summary Table: The table below shows the percentage of the Maribyrnong catchment that falls into each scoring category. See scoring method for more information.
Forested upper catchment
Mostly in the mid-catchment of the Maribyrnong River
Medium density urban and suburban sites
Densly populated urban and industrial sites and the lower Maribyrnong River
The routine monthly monitoring at 16 sites gives us information for about 79 per cent of the catchment. The remaining 21 per cent of unmonitored catchment is mostly rural and would typically score ‘Fair’ for this region.
The results show that water quality in the Maribyrnong catchment is generally ‘Fair’. We can see a clear pattern throughout the catchment, where the water quality scores reflect the impacts of various land uses.
Waterways in the forested areas of the upper catchment, such as Barringo Creek, see little impact from catchment disturbance and water quality there is ‘Very Good’. Similarly, two sites located a short distance downstream of undisturbed catchment (Riddells Creek and Jacksons Creek) scored ‘Good’. Waterways in other parts of the upper catchment that are in agricultural areas, such as Jacksons Creek and Deep Creek, scored ‘Fair’. In these areas, agricultural runoff is a major source of sediment and nutrient pollution in rural waterways, which lowers water quality.
Only 10 per cent of the land in the Maribyrnong catchment has been urbanised, which means that the water quality is generally better than in other more urbanised catchments. However, waterways in the catchment’s urban areas are experiencing the effects of pollution and stormwater associated with residential and industrial development. As such, we see that water quality in highly-urbanised regions of the catchment rated ‘Poor’ and ‘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.
Looking at the scores for the Maribyrnong going back to 2000, we see a trend of improvement in water quality. Changes in water quality over time can often be attributed to both weather and human activities.
When the drought broke in 2010/11 we saw more sustained flows in the waterways throughout the catchment. This increase in flow appears to have had a positive impact on water quality, as shown by the increase in the water quality score moving from ‘Poor’ to ‘Fair’.
The trend of improvement over time may also be due to the relatively low level of urbanisation in the catchment along with improvements to irrigation and agricultural practices over the past decade.
Improvements in water quality also have positive flow-on effects to the plants and animals that rely on waterways. Improvements to water quality along with habitat development appear to have encouraged platypus breeding in Jacksons Creek, a tributary of the Maribyrnong River where platypus surveys indicate that juvenile platypus numbers are at their highest in at least five years.
The following figures show a comparison of scores for each identified water quality indicator in the catchments and Port Phillip Bay.