Port Phillip Bay EPA water quality
The table below shows the average of all samples of the EPA's beach report enterococci (bacterial) sampling results from December 2013 to February 2024.
Location -> Average (orgs/100ml) -> Num of Samples
Altona -> 95 -> 185
Aspendale -> 57 -> 117
Aspendale Life Saving Club -> 55 -> 53
Beaumaris -> 101 -> 183
Black Rock Life Saving Club -> 51 -> 166
Blairgowrie -> 65 -> 196
Brighton Life Saving Club * - > 63 -> 154
Canadian Bay -> 112 -> 209
Carrum Surf Life Saving Club -> 149 -> 178
Dromana -> 90 -> 208
Eastern Beach -> 95 -> 188
Elwood * -> 186 -> 188
Frankston Coast Guard -> 172 -> 193
Frankston Surf Life Saving Club -> 182 -> 220
Half Moon Bay * -> 42 -> 207
Hampton * -> 73 -> 182
Mentone * -> 139 -> 214
Mordialloc * -> 147 -> 210
Mornington Life Saving Club -> 208 -> 200
Mount Martha -> 33 -> 163
Port Melbourne Beach * -> 188 -> 217
Portsea - > 19 -> 151
Rosebud -> 64 -> 171
Rye -> 168 -> 183
Safety Beach -> 59 -> 207
Sandridge -> 137 -> 198
Sandringham -> 57 -> 193
Santa Casa -> 27 -> 169
Seaford * -> 69 -> 206
Sorrento -> 50 -> 210
South Melbourne LSC * -> 88 -> 199
St Leonards -> 69 -> 184
St.Kilda -> 235 -> 214
The Dell -> 135 -> 184
Werribee South -> 134 -> 185
Williamstown * -> 58 -> 183
It is interesting to note some locations receive extraording readings at certain times. I assume this is from large rain fall events flushing out rivers or drains.
You can click locations marked with * to see the more detailed data graph. (This shows reading averages by Month, not every single reading).
If you are interested in a location data not shown, please let me know via the comments and I will update it.
Also, what do you think about the high readings for your location? Do they correspond to extreme rain fall events? Please let us know in the comments too.
Is it worse in summer? Below we averaged all EPA sample readings for all locations by month (scale on left). Taken as an average all across the Bay it does appear that spring is worse. The bacterial sample readings for October, November and December are higher in these months, where as the sea water temperatures are highest in January, February and March. So it's worse in Spring., not worse in Summer.
We can compare it somewhat against the Melbourne mean rainfall by month which is shown in yellow (the scale is in mm on the right). Although, this is the Melbourne area rainfall, not the whole Port Phillip Bay area. Port Phillip Bay receives water from six major catchments: Yarra, Werribee, Maribyrnong, Dandenong, Mornington, and Bellarine.
Port Phillip Bay Circulation and Wind Direction.
I do not know what difference the general circulation of currents in the Bay makes to how long rain water run off would stay closer to shore.
For example, from December to February there is a general clockwise rotation of currents around the Bay.
From June to August there are two opposing eddies. See image on the right.
Further, the wind strength and direction would have impacts depending on whether there are offshore or onshore winds in respective locations as these create waves energy and circular motions.
Further analysis is required, perhaps at a specific location, to determine the relationship between rainfall, temperature and bacterial levels. Would you like to do that for your favourite swim site?
Mentone Averages
A regular swimmer from Mentone asks, (below in the comments), is bacterial sample readings getting worse over time?
On the right I have produced 2 graphs of the readings from Mentone. The first graph contains the average of all samples by year from Mentone from 2014-2023.
To better determine any trend over time, I wanted to exclude data outside the standard deviation of the dataset for Mentone. This is the second graph. From both these graphs, I don't think we can conclude that the sample readings of bacterial org/100ml are getting worse over time.
What do you think?
Article by John Scanlon.
You can also use 'About - Contact us' for feedback or further questions. Below is the link to the source EPA data.