Queens Park has been an oasis in the western suburbs since the 1850s, a small lake surrounded by greenery in the heart of Moonee Ponds. On a fine day, the park fills with locals looking for peace at lunchtime, to walk the dog or relax in the shade.

What they don't know is that this idyllic spot is also one of the most seriously contaminated wetlands in Melbourne. Copper, lead, mercury, nickel, zinc and petroleum waste are concentrated at levels rated potentially toxic or highly toxic to aquatic life in the sediment on the edge of the lake.

Across the city, Hedgeley Dene Gardens in Malvern East is a park and pond nestled among leafy streets and million-dollar homes. The wetland at its centre is so contaminated by petrochemicals - 20 times the level considered toxic to aquatic life - that any sediment removed from the water could be classed as hazardous waste under Environment Protection Authority guidelines.

Foden Reserve in Campbellfield is one of the most heavily polluted wetlands in the city, the result of widespread illegal dumping in the area. After a strong rainfall, highly toxic concentrations of heavy metals and hydrocarbons can wash downstream to Jack Roper Reserve, which until recently was a popular fishing area and hosted a summer sailing club for the disabled.

Queens Park lake. Photo Luis Enrique Ascui

Melbourne's nearly 700 "constructed" wetlands and stormwater catchments were originally built to manage flooding, and pollutants such as nitrogen, before they entered major waterways like the Yarra River and Port Phillip Bay.

But over 30 years, many have evolved into suburban parks and green spaces that have become important wildlife reserves and popular recreation spots close to homes, schools and businesses. And many have become reservoirs of toxic levels of contamination.

Pollution caused by decades of intense urbanisation is being washed by rainfall into these wetlands or illegally dumped down drains to be flushed through the city's stormwater network.

It might be mercury leaking from improperly stored electrical waste; chemical spills from factories; ruptured sewer lines; motor oil tipped down drains; zinc degrading from tyres and roofs; water leaching through rubbish piles or the illegal dumping of toxic waste.

"(The) levels of contamination are really concerning and in many cases dangerous to aquatic life," said Mark Wakeham, chief executive of Environment Victoria.

"Wetlands all over Melbourne are contaminated. North, south, east and west, not just in well-known industrial areas where people might expect contamination."

Melbourne Water, which is responsible for managing the wetlands, rates the risk to public health from heavy metal and petroleum contaminants as "low", and says the system is working as it should.

"Constructed wetlands are designed to act as environmental 'kidneys' for Melbourne and capture the pollutants that wash into our stormwater drains from roads, hard surfaces, parks and gardens," said Charmaine Quick, Melbourne Water's executive general manager for service delivery.

It's a conclusion echoed by regulator the Environment Protection Authority, which also sees no immediate human health threats provided members of the public follow advice not to drink or swim in water in the wetlands.

Oil dumped into Melbourne's stormwater system. Photo: Supplied

The toxicity guidelines are based on tests conducted on insects and aquatic organisms that cannot be extrapolated to humans, the agencies say.

But there are signs the stormwater system has become so efficient at trapping contaminants that the wetlands are becoming ecological toxic hotspots that regulators are ill-prepared to handle.

In 2015, amid mounting concerns about contamination, Melbourne Water funded a study of 98 wetlands around the city, which were tested for hydrocarbons (petroleum) and heavy metals including chromium, mercury, copper, zinc, lead and nickel.

The survey found the sediment in 65 wetlands contained at least one contaminant at a concentration highly toxic to aquatic life under government guidelines, according to an academic paper published by the University of Melbourne's Centre for Aquatic Pollution Identification and Management (CAPIM).

A number of wetlands contained several heavy metal and hydrocarbon contaminants at levels that were up to 20 times thresholds for high toxicity.

The wetlands are spread across Melbourne, often connected by stormwater infrastructure that transfers pollutants far from their source.

At Albert Park Lake, copper, lead, nickel and zinc have been found at levels deemed to be potentially toxic to aquatic life. Contamination from petrochemicals in the popular fishing and boating spot is double the level considered highly toxic.

Mr Wakeham said it was alarming the state government encourages recreational fishing in some of the wetlands, including programs stocking rainbow trout at Albert Park Lake.

"While Parks Victoria advises catch-and-release rather than eating fish caught at Albert Park, we need much clearer advice from health authorities about whether eating fish caught at contaminated wetlands is a human health risk," Mr Wakeham said.

Parks Victoria said "traditional contaminants" known to accumulate in fish such as mercury and cadmium were "below the levels of concern" for the lake.

"The sediment results reported in the study indicate Albert Park Lake is one of the least contaminated which shows the stormwater treatment ponds are working," Parks Victoria chief operating officer Simon Talbot said.

Jack Roper Reserve Lake wetland in Broadmeadows. Photo Luis Enrique Ascui

Handling the sediment in many of the wetlands CAPIM surveyed - if they were dredged and dumped on land - would require permits from the EPA to legally transport and dispose of the soil at special landfills because it would be classified as hazardous.

"While they might be really nice to look at on the surface, often what's under the surface is not so nice," said the CAPIM study's lead researcher Dr David Sharley. "Heavy metals can't be seen so it's often a case of out of sight, out of mind, but these wetland areas are becoming ecological traps for wildlife.

"This is a long-term problem, especially when you consider how many other contaminants are already out there."

Melbourne Water and the EPA say the sediment poses no risk to humans. However, the circumstances can change when it is removed from the water.

In late 2014, Melbourne Water began routine maintenance on Stony Creek in Yarraville, which feeds into the Yarra River after passing through a network of wetlands and reserves stretching back to St Albans.

The work involved dredging and stockpiling sediment at several points on the stream's edge. But an EPA test found the sediment contained asbestos, lead, zinc and hydrocarbons. The stockpiles were fenced off and sign-posted as a potential health threat.

Melbourne Water was issued with four clean-up and risk assessment notices as part of a six-month EPA enforcement operation at the contamination sites.

The hazard classification given to the Stony Creek sediment by the EPA would also apply to more than 50 wetlands sites identified by the CAPIM study.

Different standards for fish

The Jack Roper Reserve is a park and playground with a small lake in Broadmeadows, just north of the Western Ring Road. It's one of the few places within city limits where - until recently - it was considered safe to fish.

In July the lake was closed to all forms of recreation after tens of millions of litres of contaminated water flowed toward Jack Roper Reserve as firefighters battled a massive blaze at a recycling plant in Coolaroo. Hundreds of fish died and testing also revealed the presence of E.coli bacteria.

But the lake was significantly polluted long before it was officially closed.

Jack Roper sits at the end of a six-kilometre stretch of Merlynston Creek, which is essentially a chain of stormwater drains and culverts that originates in the city's heavily industrialised north and flows past factories, warehouses and residential neighbourhoods in Campbellfield, Coolaroo, Dallas and Broadmeadows.

Close to its origin is a one-hectare dot of green space in the middle of a massive industrial estate known as Foden Reserve, one of the most heavily polluted wetlands in the city. Highly toxic concentrations of five different types of heavy metals and hydrocarbons exist there.

The site is well-known to the EPA because industrial waste illegally dumped or accidentally washed down stormwater drains in the area passes through Foden before entering Merlynston Creek and, after a strong rainfall, washes down to Jack Roper Reserve.

The Victorian Fisheries Authority (VFA) used to stock 900 rainbow trout in the lake at Jack Roper each year, timed to coincide with school holidays and an annual fishing event. The lake has also been used for years as a summer sailing club for the disabled, and boats are launched from a ramp located close to a major stormwater pipe.

Peter Hughes, with dog Rosie. Peter is a local resident, and frequents Queens Park. Photo: Daniel Pockett

The VFA stopped stocking fish in Jack Roper in 2014 after Melbourne Water flagged concerns about the water quality following several serious "pollution events" upstream. Latex, mercury and motor oil have all been dumped in substantial quantities.

The Fawkner & Merlynston Angling Club used to run a 'kids-come-fishing day' at the lake, which was permanently cancelled in the wake of the VFA's decision.

"That's when it all came to a head. We were hearing there was something wrong with the fish - they didn't smell right and were discoloured," said club spokesman Len Bird. "It's very frustrating because it was a good venue and something unique for the area."

Yet fishing and boating were allowed to continue at Jack Roper, right up until the Coolaroo fire in mid-July.

That was also nearly six months after the CAPIM study found the wetlands at the northern end of the reserve - where Merlynston Creek meets the lake - contained high concentrations of zinc and hydrocarbons, as well as levels of copper, lead, mercury and nickel that are potentially toxic to aquatic life.

A Melbourne Water spokesman said the lake would be reopened when the pollution fallout from the Coolaroo fire dissipated.

The wash-up

The University of Melbourne's CAPIM study was published in a scientific journal in February but the findings received no publicity from Melbourne Water, its primary financial backer.

When initially contacted by The Age about the study, Melbourne Water refused to say whether it had a plan to remediate the contaminated wetlands. Nor would it comment on the level of toxicity necessary for it to issue a warning about coming into contact with the sediment.

"Melbourne Water believes the public health risks associated with pollutants in wetlands are low," EPA official Charmaine Quick said.

"We hope the results of the study encourage Melburnians to think about what goes into stormwater drains and to always follow the directions when using or disposing of household chemicals."

Ms Quick said a "rigorous maintenance program" was in place to manage the constructed wetlands.

However, the agency later acknowledged that no wetlands had been cleaned specifically due to contamination. Melbourne Water added the results of the CAPIM study would now be used to help determine if "triggers" should be designed for rehabilitating wetlands based on pollution levels.

But Mr Wakeham, of Environment Victoria, said Melbourne Water's approach represented poor risk management.

"Given that these sites will deteriorate further, it is unacceptable that the EPA and Melbourne Water have no guidelines for when intervention will be required."

The EPA, which is responsible for overseeing the disposal of hazardous waste in Victoria, said Melbourne Water had no obligation to clean the wetlands even though it was aware of heightened contamination levels from the study.

"The EPA liaises with organisations such as Melbourne Water so they better understand the environmental risks that they own and are responsible for," EPA chief environmental scientist Dr Andrea Hinwood said.

Both Melbourne Water and EPA stress the most important tactic for protecting Melbourne's waterways and wetlands is stopping pollution before it enters the system.

Melbourne Water has continued to fund research and programs to help end contamination, including new sampling technology that can identify the exact source of pollutants from high-risk industrial areas.

The technology was developed by CAPIM scientists, including Dr Sharley, through a consultancy, Bio2Lab, contracted by several councils as part of enforcement and education programs that have successfully targeted individual polluters.

The EPA has also funded a $4.8 million project that embeds EPA officers in 13 Victorian councils in an bid to improve enforcement efforts.

In the meantime, the regulator's primary advice remains that no one should drink from or swim in the waterways.

cvedelago@theage.com.au