A new study shows Victoria's network of wetlands can lock away a year's worth of carbon emissions for a city the size of Geelong.
It's common knowledge that trees help neutralise a carbon footprint and it turns out wetlands are also doing their share of soaking up gas.
A team of Victorian researchers estimate a group of the state's inland swamps, lagoons and marshes are erasing the entire footprint left by the people of Geelong.
A Deakin University study, published in the Global Change Biology journal on Tuesday, found the wetlands soak up three million tons of carbon dioxide each year.
That figure is equivalent to the yearly greenhouse emissions of 185,000 people, roughly the population of Geelong.
Victoria's inland or non-tidal wetlands are an integral part of Australia's carbon budget and dwarf the more recognised contribution of some native forests, lead researcher Paul Carnell said.
"While a lot more is known about how trees suck up and store carbon, freshwater wetlands can actually sequester 20 to 40 times more carbon than forests on dry land," he said.
Victoria has about 530,000 hectares of inland wetlands - including marshes, peatlands, pools, billabongs and lakes - making up about 2.33 per cent of the state's landmass.
Researchers analysed the soil of more than 100 wetlands across the state and estimated 68 million tons of carbon - worth about $6 billion under Australia's most recent carbon price - is being stored.
Mr Carnell said the wetlands' lack of oxygen makes it difficult for carbon to be broken down and re-released into the atmosphere, allowing the material to be locked away for years.
"It's the reverse process of digging up and burning coal or oil, here wetlands are taking that gas and putting it back into the ground," he explained.
But Victoria's wetlands network has shrunken by more than a quarter since European settlement, the study estimates, sending 16 million cars'-worth of annual emissions skyward.
"This means disturbance and loss of wetlands has the potential to release significant quantities of CO2 back into the environment," Mr Carnell said.
Due to a lack of data, the federal government does not account for freshwater wetlands as a source for official carbon savings.
Marine science expert Peter Macreadie, commenting on the study, said further research is required to quantify the wetlands' methane emissions as they could offset the network's carbon-cloaking benefits.