Underwater ecosystems at risk of ‘dying off’ if Wellington’s sewage leak continues

Monday, 9 February 2026

Workers and volunteers scoop up waste and debris at Tarakena Bay Beach after an equipment failure at Wellington’s Moa Point wastewater plant sent untreated sewage into the sea, prompting health warnings and beach closures.

A marine biologist has warned that millions of litres of raw sewage being dumped into Wellington’s south coast by the city’s broken wastewater plant could “kill off” vitally important underwater ecosystems.

Victoria University’s Christopher Cornwall said native seaweed and kelp were extremely sensitive to the high levels of nitrogen found in wastewater, while invasive species thrived on it.

“The kelp forest could end up dying off in patches around there. And if that happens, then certainly the ecosystem will be damaged, and it could take a very long time to recover,” Cornwall told Stuff.

Toilet paper and condoms washed up on Moa Point in Wellington on Wednesday.

The kelp forests off Wellington’s south coast were among the “most productive ecosystems in the world”, providing a habitat and food for other species including pāua, kina, crayfish and larger finned fish like cod.

“If we think about the species that would replace the native kelp, that thrives on nitrogen, that's mostly the green tide algae and the wakame, they don't provide the same sort of habitat,” he said.

Christopher Cornwall, Victoria University senior lecturer in marine biology, warns that accelerated levels of nitrogen in wastewater could damage kelp and native seaweed.

The sewage could also have an “adverse and almost unpredictable impact” on marine species, with the microbiome, or gut health, of seaweed and sponges shifting to harmful microbes, which could cause bacteria and disease.

“I think people should be really concerned if this happens again or continues to happen in any frequency. It's very unheard of in the developed world for something like this to occur,” he said.

Since Wednesday, when its long outfall pipe backed up after heavy rain, the Moa Point wastewater treatment plant had been spewing tens of millions of litres of raw sewage into the ocean each day.

The type of native seaweed found on Wellington's south coast.

Wellington Water said it was now using the long outfall pipe again, and was able to screen the wastewater for wipes and sanitary products, but the water was still not undergoing biological or ultraviolet treatment before being discharged.

Dive Wellington taking people scubadiving at the Taputeranga Marine Reserve prior to the plant breakdown.

“Our priority is getting the site as safe as possible for a closely managed entry to evaluate the extent of damage to the plant, test the equipment, and determine what needs to be repaired or replaced,” it said in a statement.

Dive Wellington owner Dave Drane said the south coast could handle small amounts of sewage, but the levels seen risked “settling in rock pools and smothering” sealife at the the Taputeranga Marine Reserve he regularly dived.

“We have spent years trying to get the reserve to what it is, and this could ruin it. One or two days we can handle, but for weeks and weeks of not being able to dive on our coast, it's embarrassing,” he said.

Island Bay Divers owner Tim Walsh taking a crew out at the reserve.

Tourists were contacting him saying they wanted to dive at the reserve, however he did not know when it would be safe again, and said the whole fiasco was “tarnishing Wellington’s image”.

“I'm getting back to them and saying, actually, sorry, we've had a sewage spill, so I can't take you diving in the marine reserve. It’s like we are a third world country, answering emails like that,” he said.

Island Bay Divers’ owner Tim Walsh said his business was suffering too, but he was more concerned by the impact the sewage would have on marine life that would “try out anything” if hungry.

“The impact on the marine life, like fish and birds, they could be eating stuff that they will choke on and could kill them. There's a possibility that even marine mammals, like seals or stuff like that, could come to harm as well,” he said.

Last week Wellington Mayor Andrew Little confirmed an inquiry into Wellington Water’s handling of the breakdown at the plant would be taking place, while Prime Minister Christopher Luxon has said he would also support one.

Cornwall said it was imperative authorities took the environmental impacts as seriously as how the mishap was managed, given the marine reserve was a “jewel”, and a protected area.

“Now is the prime time to actually address this and figure out, well, how was it even possible for this to happen? Because I don't think something like this has occurred anywhere else,” he said.