Invercargill estuary 'smells like Rotorua'

Dry conditions around Invercargill have made the area smell like Rotorua, Environment Southland says.

The smell coming from the New River Estuary has raised the ire of some residents who have complained to the organisation.

Environment Southland coastal scientist Nick Ward says he was not quite sure of the cause, but it was most likely because of the relatively warm, dry conditions in the region.

“It’s something we’ve been investigating but it’s a work in progress,” he says.

Mr Ward recommended people avoid water-based activities, stay away from areas which smell bad and where they can see black sediment. 

The New River Estuary has been experiencing excessive nutrient and sediment input from waterways in the past few years, he says.

The change in nutrient levels created good growing conditions for red and green algae, but were not ideal for fish habitat species like seagrass.

“This prolific growth results in lots of organic matter which rots down,” Mr Ward says.

The bacteria which causes the organic matter to rot eventually uses up oxygen and eventually other compounds including carbon dioxide and sulphate.

Mr Ward says the sulphate breaks down to form hydrogen sulphide which “smells like rotten eggs”.

“It’s the same smell you’ll get in Rotorua,” he says.  

Low river levels, warm conditions and lower tide levels mean more of the black hydrogen sulphide sediment is exposed and more of the gas it produces is able to disperse.

“That’s why people are picking up on the smell,” Mr Ward says.

3 News

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