Williamstown beach has dropped from second to 14th in Port Phillip Bay water quality rankings, according to new data released last week.
And Altona fell from 14th to 19th among the 36 beaches ranked under the Environmental Protection Authority (EPA) Beach Report program between November 1 and April 10.
Williamstown Beach was closed after a bright orange discolouration was reported on December 10.
An alert was issued for an algal bloom but that was removed the following day when the bloom was broken up by wind and tides.
Altona beach was subject to an EPA investigation after its pollution hotline received about 400 calls between January 10 and 15 about a smell described as sewage or seaweed.
EPA executive director Damian Wells said the most likely cause was seaweed and exposed mudflats during an extreme low tide along the coastline between Altona Meadows and Werribee South.
But Hobsons Bay council remained unconvinced and commissioned its own expert to conduct tests.
The results of those tests are expected next month.
Storm water
EPA applied sciences group manager Anthony Boxshall said rainfall in the catchment was the main influence on beach water quality.
“Rain washes everything down off the streets and through the stormwater system and out into the bay through drains and creeks,” he said.
“People walk their dogs and leave what the dogs do on the side of the path.
“There’s also a lot of birdlife around Altona, particularly with seagrass … and that can bring pollution.
“And then on the land we’ll find leaks, sometimes on public loos near the beaches.
“And then you’ve got construction sites portaloos, and they can leave a bit [of pollution].”
The beach report data was released as the Minister for environment, climate change and water, Williamstown resident Lisa Neville, launched the EPA’s new marine monitoring boat, bar-ba-ka.
The new boat, which is moored at Williamstown, will help the EPA investigate marine issues, respond to environmental emergencies, identify pollution hotspots and manage compliance investigations.
Nine Port Phillip beaches were in equal first place for water quality in the latest EPA rankings – Hampton, Seaford, Portsea, Canadian Bay, Sandringham, Elwood, Rosebud, Santa Casa and Black Rock.
