Melbourne Water officially say this (amongst other things);
http://www.melbournewater.com.au/content/rivers_and_creeks/river_health/river_health.aspAnalysis from 2005 shows that of the rivers and creeks in the region:
25% are in good or excellent condition
31% are in moderate to poor condition , and
44% are in poor or very poor condition.
www.melbournewater.com.au/content/rivers_and_creeks/the_rivers_and_creeks_system/history_of_our_rivers_and_creeks.asp?bhcp=1Today, urban development is more sustainable in its approach, and water sensitive urban design is being introduced into suburbs to protect water quality and river and creek health. Waterways are now also valued in the urban landscape and are generally included in open spaces for new developments.
However, continuing urban growth has led to a decline in river health. As in the past, it will be a challenge to protect rivers and creeks as the lands around them change.
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Legal dumping of contaminated substances is very expensive, which I'm sure leads some dodgey practitioners towards illegal dumping.
I know Sydney Water have spent a reasonable amount of money inserting some catchment and settlement points within the stormwater systems, to assist with catching some of the pollutants, and then collecting prior to it getting into the water ways. But then you have to wonder, what happens to it at the legal dump sites.... but the EPA and the dump operator
should have that end under control (??).