Yarra
& Bay

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Port Phillip Bay

Land Use

Urban

Rural

Forest

Water Quality Index

Very Good

Good

Fair

Poor

Very Poor

See the ‘Port Phillip Bay’ page for a detailed description of the Bay.

Report Card for July 2014 – June 2013

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.

Catchment Bay

Area Score
77%

Very Good
Near-natural high quality waterways

Entrance, Dromana and central bay

22%

Good
Meets Victorian water quality standards

Near-shore areas

1%

Fair
Some evidence of stress

Newport

0%

Poor
Under considerable stress

0%

Very Poor
Under severe stress

Routine monthly monitoring across 8 sites accounts for 100% of the bay

What do the results mean?

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.

Bar chart showing WQI and indicator scores for Port Phillip Bay Bar chart showing WQI and indicator scores for Port Phillip Bay

PortPhillipBayEPAVictoria.png Healthy seagrass meadows are an indicator of good water quality in Port Phillip Bay. Source: Parks Victoria

Changes over time

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.

Plot of WQI history for Port Phillip Bay

Plot of WQI history for Port Phillip Bay

Compare to other Catchments

The following figures show a comparison of scores for each identified water quality indicator in the catchments and Port Phillip Bay.

Diagram of nutrient score history for catchments and bay

Diagram of oxygen score history for catchments and bay

Diagram of water clarity score history for catchments and bay

Diagram of salinity score history for catchments and bay

Diagram of algae score history for catchments and bay

Diagram of metals score history for catchments and bay

Program Partners

Department of Environment and Primary Industries Environmental Protection Agency Melbourne Water