TWEED Shire Council has confirmed sewerage was not to blame for a pungent smell described as "rotten eggs" emanating from mangroves at Terranora today.

Residents around the Terranora Inlet and Oxley Cove complained to the council when odours that smelt like sewage had not dissapated after several days.

The source of the smell was found to be fruit dropped by mangroves, which produces hydrogen sulphide gas when decomposing, the same "rotten egg" gas which is given off by sewage.

"The mangroves drop fruit or propagules, which are actually live young plants," the council's waterways program leader Tom Alletson said.

"The fruit which didn't succeed in taking root is now beginning to decompose and is being consumed by bacteria in an environment which is lacking oxygen - this produces the hydrogen sulphide gas and black smelly water."

Water testing has proven negative for the presence of ammonia, which is a tell-tale sign of the presence of sewage in waterways.

Inspections of sewage pump stations and sewer mains have found the sewerage system to operating normally.

"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," Mr Alletson said.

Anyone who still has concerns about sewer-like odours in their area can call council on 02 6670 2400.