Mass deaths at Waipu¯
Thousands of fish, eels and plants die at estuary — it’s believed it’s from algal bloom
Hundreds of thousands of marine life are dead and Waipu¯ residents are being driven out of their homes with by a stench described as rotten eggs and dead bodies believed to be caused by recurring algal bloom.
What’s more, a wildlife refuge within the affected area is an integral feeding zone for protected bird species.
The Waipu¯ estuary lagoon, south of Johnson’s Point, has been described as a “dead zone” with lifeless marine species including eels, fish and plants. What remains alive are said to be beaching themselves, gasping for breath in an attempt to escape the black oxygen-depleted waters, believed to be from trapped and rotting algal bloom.
The east coast beach has been plagued by a thick red algal bloom carpeting the beach since around 2010. It has since washed up every summer with some years worse than others. However, this is the first time the estuary has been affected.
Believed to be called Spyridia filamentosa, it is particularly prominent when storms come in from the east. As the tide recedes, it becomes trapped, stagnates, and starts to rot and smell in the sun.
Waipu¯ Cove resident of 20 years David Lourie, who has a background in horticultural science, said there were hundreds of thousands of dead fish in the estuary area. “From my perspective, it’s been a massive die-off. It smells like rotten eggs and that smell is created by a gas called hydrogen sulphide generated by a breakdown of organic matter and if it gets into the water, it kills.
“I’m not a professional but I think they died from a lack of oxygen and the fish that are alive have been driven ashore trying to get their heads out of the water. I don’t think it’s a [direct] threat to the birds but the fish are an important food source for a lot of the birds.”
Established in 1969, the Waipu¯ Wildlife Refuge, which he estimates to be an “elongated square kilometre”, is within this area and has international significance as a nesting area for New Zealand dotterels, variable oyster catchers and New Zealand fairy terns.
Northland Regional Council’s Rick Stolwerk, who represents the council’s Coastal South Constituency, said the council was notified about dead eels and fish in the lagoon area of Waipu¯ estuary last weekend. A staff member investigated this week and, he said, it appeared bacteria were breaking down a large quantity of dead and rotting red algae (seaweed) that had washed into the upper parts
of the lagoon from Bream Bay and become trapped. “In the upper area of the lagoon there’s very little circulation and exchange of water with the open coast and, once again, our staff recorded very low dissolved oxygen concentrations in the lagoon.
“As far as council’s aware, the algae itself isn’t toxic or harmful as such, but it obviously affects the amenity value of the area and can definitely generate unpleasant odour as a result of the generation of hydrogen sulphide gas, which smells like rotten eggs.”
Council coastal resource scientist Richie Griffiths said NRC had advised the Northland District Health Board of the situation to assess if the gas generation had any public health implications. The Department of Conservation had also been informed, as had local tangata whenua
Patuharakeke. Griffiths said it was unclear if the algal bloom had entered as a large volume or a small amount that had multiplied over time, but warm and relatively shallow conditions in the lagoon were likely initially favourable for the red algae to continue to grow. However, that had changed once the algae began to die with its decomposition consuming much of the oxygen in the water.
“This can lead to a rapid decrease in dissolved oxygen levels that will cause stress and mortality to other marine plants and animals. The dead and decaying plants and animals will also fairly rapidly cause an unpleasant smell.”
Griffiths said he had been at the lagoon on February 11 for an unrelated reason and noticed a small amount of the algal bloom. “It was observed but not enough for me to be alarmed. It’s come in at some point and it’s possibly been in there over the summer in varying degrees. The problem is when it starts to die because there’s no flushing there so there’s very little water movement.”
As a result, he said the issue is likely to get worse before it gets better. However, while unpleasant, the process was a natural one and was a typical cause of decreased dissolved oxygen levels in water.
Griffiths and Stolwerk said the problem is likely to persist until the algae has broken down or is flushed out in an autumn storm with Griffiths adding that, while he can’t guarantee it won’t happen again, this was the first time it had happened in this area in his 10 years at the NRC.
Stolwerk agreed there was no way anybody could guarantee it would not happen again. “[The river] used to come out at Waipu¯ Cove in the 1880s when it burst through the dune approximately where the river mouth is today. A teatree groyne was constructed to keep it open. This means that the area south of the existing groyne cannot now naturally flush, it will have to wait for a high rainfall event. The only thing that can be done is to establish a monitoring programme that can then be used to model the possible source of the algae. Although this offers no immediate solution, it does offer hope for a long-term sustainable outcome.”
Waipu¯ Cove estuary resident Judith Cullen had returned from holiday to her waterfront home on Friday afternoon to what smelt like dead bodies. She and her neighbours had their windows closed due. “I’m actually considering heading out for the afternoon just to escape it.”
Joe Neho and his son Santana had driven to the estuary from Pipiwai on Tuesday and arrived to what Neho described as a “dead zone”.
“We drove to Waipu¯, past Johnson’s Point Rd, and got to our usual spot and my son and I walked down with the container and net and got near and there was just this strong septic smell. “There were fish dead everywhere – lots of dead eels, flounder, parore, lots of those really small fish and dead crabs. It was like a dead zone.”