I wonder if this final comment at the end of the article answers the question why there was no significant public notice given:

"Melbourne Water spokesman Dr Paul Pretto said the huge amounts of water moving through the system that day would have diluted any sewage that was dumped around the city. ''The practical impact on river health is extremely low and it would be washed out very quickly,'' he said."

It sounds like a typical "beat up" article that then concedes right at the end that actually there's not really an issue at all.

Then again, it depends on what "...extremely low..." and "...very quickly..." mean...and yes, it might wash out of the rivers quickly but what about the Bay where the rivers run out to?

...and it's all pretty academic anyway..there's no bloody wind!!!! ;)