City investigation finds mangroves and not sewage to blame for northern suburb stink

Council have found the reason why a putrid smell has been infiltrating the Gold Coast’s northern suburbs over winter. Find out here

The cause of the Gold Coast’s great suburban stink has been revealed after a council investigation.

An odour monitoring program has confirmed that the strong “rotten egg” smell regularly experienced by Monterey Keys residents was caused by natural processes in the adjacent mangroves forest.

Helensvale-based councillor Naomi Fowler said the investigation had cleared the Coombabah Sewage Treatment Plant of being the villain.

Gold Coast City councillor Naomi Fowler with city environmental staff checking the monitoring of mangroves in the Coombabah Wetlands.

“Between March and November 2024, the City undertook comprehensive monitoring of hydrogen sulphide levels at both the mangroves and the Sewerage Treatment Plant,” Ms Fowler told this masthead.

“Results showed that concentrations at the mangroves are, on average, 16 times higher than those at the treatment plant, particularly during king tides and cooler weather when the gas stays closer to ground level.

“The City is undertaking verification monitoring at the moment and is anticipating similar results.”

Ms Fowler said council was not aware of any issues with its sewerage infrastructure that would lead to increased odour levels.

Many residents have welcomed the update by Councillor Fowler.

Gold Coast City Council environmental officers monitoring the mangroves in the Coombabah Wetlands.

“Not only for listening, personally checking, but making results available as well as a fabulous explanation. If only all councillors were of that calibre,” a resident said

But others want some of the mangroves filled in by council to stop the stench.

“This does not make any sense. Why would you build properties that cost millions of dollars to live in when you’re subject to being kept inside and indoors due to the stench,” a resident wrote.

Residents in late 2023 raised concerns about upgrades to council’s water treatment plant after discovering hundreds of fish kills around Monterey Keys.

The Coombabah Wetlands and mangroves being monitored by the Gold Coast City Council.

Others speculated that heavy construction works for the new Coomera Connector highway was contributing to poor water in canals.

In a Facebook update to residents, Ms Fowler said she had recently “pulled on the gum boots” and visited the wetlands with City environmental scientists.

“Unfortunately, because the wetlands are a protected environmental area, there’s no treatment available to reduce or remove the odour,” she said.

“We inspected the odour-monitoring logs, which record data every 10 minutes, and cross-checked this with readings from the same odour-monitoring logs at nearby sewerage plants.

The key findings included:

* Recent rainfall and high tides have disturbed a significant amount of organic matter.

* There has been a large drop of mangrove seeds, which increases decomposition.

* This results in more sulphide gas – the main cause of the “rotten egg” smell which does show a more intensive odour than within Sewerage Treatment Plants.

* The City’s infrastructure team has checked all pump stations and sewer lines in the area – there are no leaks or faults that the City is aware of that are the source of the smell.

Councillor Naomi Fowler with Gold Coast City Council environmental staff checking the monitoring of mangroves in the Coombabah Wetlands.

“I completely understand how unpleasant this is for residents. While we can’t intervene in protected wetlands, I want residents to know the City has done their due diligence and will continue monitoring the situation,” Mr Fowler said.

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Originally published as City investigation finds mangroves and not sewage to blame for northern suburb stink