See the ‘Port Phillip Bay’ page for a detailed description of the Bay.
This Report Card provides us with a snap shot of water quality in the Bay from 1 July 2013 to 30 June 2014. The quality of the water is rated by combining the results of five standard water quality parameters: nutrients (nitrogen), water clarity (total suspended solids), dissolved oxygen, salinity (conductivity) and algae (chlorophyll-a).
Summary Table: The table below shows the percentage of Bay area that falls into each scoring category. See scoring method for more information.
Entrance, Dromana and central bay
Routine monthly monitoring across 8 sites accounts for 100% of the bay
The results show that water quality in the Bay is generally ‘Very Good’. They also show that water quality in the Bay gets better the further away from river mouths and stormwater outlets.
Monitoring at Newport showed the poorest water quality result for the Bay (‘Fair’). This result can be explained by pollutants being flushed through the mouth of the Yarra through this site. In contrast, Popes Eye has ‘Very Good’ water quality – it is far away from rivers and stormwater outlets, and it’s well flushed by clean seawater from Bass Strait.
The remaining sites showed similar patterns of declining water quality with proximity to point sources of freshwater.
Since 2000, water quality in the Bay has improved.
In years of drought and lower rainfall, such as 2006 and 2007, water quality improvements in the Bay, especially at sites close to rivers and stormwater outlets were associated with lower inputs of sediment and nutrients to the Bay.
During periods of extremely low rainfall, water quality may also decline due to increased salinity as a consequence of not enough freshwater flowing into the Bay to compensate for water lost though evaporation. This occurred in 2008 and 2009, towards the end of a long drought. The Bay’s salinity increased above the normal range for seawater.
Human activities have the potential to impact on water quality in the Bay, too. While Melbourne’s population has increased by more than 25% since 2000, water quality at most sites in the Bay has remained ‘Good’ to ‘Very Good’. This shows that sewage treatment plants have been successful in reducing the amount of nutrients they discharge into the Bay, amongst other activities.
The following figures show a comparison of scores for each identified water quality indicator in the catchments and Port Phillip Bay.