A stinking pond of heavily polluted stormwater from the streets of Mortdale provides an insight into why the environmental health of the Georges River is slipping.
The pond in the largely man-made Lime Kiln Bay Wetland at Oatley captures coarse sediments and pollutants that have got through gross pollutant traps upstream in Daisy Creek
Pollutants settle in the sediment pond before the water is further screened through a constructed wetland before running into Lime Kiln Bay.
However, during major rainfall events, stormwater pours over the top of the gross pollutant traps and flushes the pond, often together with overflowing sewage, into the river.
Environmental groups said similarly polluted stormwater was flowing into the Georges River from hundreds of creeks.
They said the state government needed to do more to address the problem.
Secretary of the Georges River Environmental Alliance Sharyn Cullis said the situation was caused by increased urban density.
“Georges River is not coping now, and the problem is only going to get worse,” she said.
“Concrete and bitumen is replacing soft ground, which is a natural filter.”
Ms Cullis said the Greater Sydney Commission’s draft regional plan for Sydney South projected at least 23,000 more homes in the next 40 years.
The 2015-16 report card by Georges River Combined Councils revealed “a slight decline” in the ecological condition of the catchment over the previous year.
The catchment received a C+ (fair) rating, but water quality in some parts, including Gungah Bay (D-) and Lime Kiln Bay (D+) was rated “poor”.
Like the standard gauge argument during last century, everyone blames everyone else and no-one is willing to spend money
Botany Bay and Catchment Alliance spokesman Brian Shaw said member groups believed the government needed to take a combined authority planning action.
“Like the standard gauge argument during last century, everyone blames everyone else and no-one is willing to spend money,” he said.
“If we are to have the urban growth proposed by Greater Sydney Commission and the state government, infrastructure needs to be put in place first.”
The Minister for Environment (before this week’s cabinet changes), Mark Speakman said most stormwater pollution “starts from local issues, such as the management of construction sites, littering, leaves, animal droppings and chemicals such as oil or fertilisers”.
“Therefore, in most cases, it is the responsibility of each and every one of us, but managed by local councils with the support of government agencies,” he said.
Mr Speakman said the state government provided more than $1 million to councils in the Georges River catchment over the past five years through a number of grants funded under the Coast and Estuary Management Program.
He said the Office of Environment and Heritage monitored water quality at swimming sites through its Beachwatch program, which provided valuable data for councils.
“Councils are responsible for improving beach water quality and river health alongside wastewater managers, such as Sydney Water Corporation,” he said.
Ms Cullis said the situation in the Lime Kiln Bay Wetland, where there had been little rain over the last month, was “a disgrace” and “as bad as it gets”.
"It’s close to a black water event, which occurs when there is little oxygen, so anything in the water starts to die as well,” she said.
“Algae feeds on the concentrated levels of nitrates and phosphates, from detergents, fertilisers and dissolving dog droppings.
“This is a little creek system that would drain from almost 100 per cent urbanised catchment, including Mortdale shopping centre.
“[Georges River Council] does its best, and comes down and cleans the GPT (gross pollutant trap) regularly and takes away mountains of litter and rubbish that comes down the creek.
“But, every time we get a really high flow event, the GPT will be over-topped so some litter will still go over the top.
“In addition, the screen allows through a lot of micro plastics, polystyrene, plastic bags, anything that is small, as well as dissolved pollutants like nitrates, phosphates and bacteria from dissolving dog droppings and grease and oil that comes off hard road surfaces.
“The problem is you have a hard surface catchment, and it’s ruining this little creek system.
“This used to be, and still is, a very valuable recreational area; people walk though here all the time, but it has just been ruined.”
Ms Cullis said answers were readily available if the government was committed to tackling the problem.
”There is a whole science around urbanised catchments,” she said.
”Environmental engineers are developing principles of water sensitive design and practical projects.”