Mangroves are the source of sewage-like smells in Tweed

10 July 2019

Rotten egg gas odour produced by rotting fruit

What’s that awful smell? If you live in the north of the Shire, it’s not a sewage spill. It’s the odour of decomposing mangrove fruit.

Council has received numerous calls from residents around Terranora Inlet (particularly the Cobaki Broadwater Village), The Anchorage and Oxley Cove reporting suspected sewer leaks causing a persistent foul odour in residential areas.

The source of the smell is fruit dropped by mangroves, which produces hydrogen sulphide gas when

decomposing - the same ‘rotten egg’ gas which is given off by sewage.

Inspections of sewage pump stations and sewer mains have found the sewerage system to be operating normally and with no ammonia present (which would be a tell-tale sign of the presence of sewage in waterways).

Council’s Waterways Program Leader Tom Alletson said the common species of mangrove on the

Tweed, the grey mangrove (Avicennia marina) began fruiting prolifically four to five weeks ago.

“Grey mangroves drop fruit at this time of year and there are masses of grey mangrove fruits stranded within the 25-hectare wetland to the east of places such as Cobaki Broadwater Village and other sections of estuary,” Mr Alletson said.

“The factors which cause the odours to become so strong at certain times are not clear, but would be related to tide, rainfall, the amount of fruit dropped in the season, frequency of tidal flushing and wind strength and direction.

“This is a natural process so Council is not able to control this issue or address any of the factors that lead to the odour problems,” he said.

Mr Alletson said mangroves are an extremely important part of the Tweed estuary which provide

habitat for fish, crabs, prawns and numerous bird species as well as acting to stabilise the shorelines. They are also protected under a number of NSW Government laws.

“While it is acknowledged that the smell generated in these areas is offensive, in almost all cases it is

entirely natural, temporary, and one of the few downsides of living in close proximity to our beautiful

waterways,” he said.

Anyone who still has concerns about sewer-like odours in their area can call Council on (02) 6670

2400.

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Caption: The rotting fruit of the grey mangrove is the source of sewage-like smells in some areas close to water in Tweed Heads.