Waituna Lagoon – closed but not forgotten

| April 6, 2024 | 0 Comments

By Jo Crack

Waituna Lagoon has now quietly closed to the sea, ironically at Easter when those who claim to be the guardians of the lagoon were not watching – DOC, Iwi and ES.

As has often been the way in the past, the lagoon has again whispered to the locals, and in a stroke of irony, by April Fool’s Day the sea had pushed up enough pea gravel to end the lagoon’s cleansing process which began on 31 January 2024 when it was mechanically opened to the sea.

Waituna Lagoon flushing to the sea, January 2024.

Prior to this, in September, lagoon levels had been high, over 2.4m, which meant the lagoon was no longer in the lagoon and instead had fanned out onto farmland, and landowners were concerned a deluge on top of an already brimming lagoon would bring significant flooding and damage. They urged ES to open the lagoon under emergency powers. That fell on deaf ears and it was at this time the landowners told ES that the lagoon would do the talking.

That is exactly what happened, the locals thought it would be a flood that would tell the story but instead the water level dropped as water seeped out through the porous gravel bar to the sea – effectively straining the usually brackish coloured water, while retaining nutrient laden sediment.

As that water level gradually dropped the algae began to dominate. The once clear lagoon was full of toxic cyanobacteria (algae) and it quickly turned a murky green.

It was horrendous to be utterly powerless watching this unfold.

But now, two months on, with the closing of the lagoon, a new cycle begins as the water, which feeds from the catchment will gradually, or possibly quickly depending on weather events, build up and replenish the lagoon.

What now worries the locals is that DOC, Iwi and ES do not appear to have learned any lessons from the near demise of the lagoon. Their joint consent application revolves around 2.5m as being the future opening level.

Historically the lagoon was opened at a level of 2.0 and then more latterly 2.2m by the Lake Waituna Control Association. The locals believe this level to be appropriate for both the health of the lagoon, allowing for more frequent flushing and to prevent flooding of farmland, erosion of feeder creeks and then resulting sediment loss.

2.3m and Ruppia

The other level of significance is 2.3m. The Lagoon Technical Group, a scientific group that consists of several coastal lagoon experts, has said that ruppia – a sea grass considered an indicator of lagoon health – could be harmed if the water level was maintained over 2.3m for more than 20 days.

ES graph which shows the length of time the lagoon was at 2.3m or above.

As it turns out they were right, the locals had noticed that by 8 September 2023 the ruppia beds were no longer healthy and thriving, there was dead ruppia piled up 18inches high in places, and by the opening of fishing season on 1 October the beds at the eastern end were all but toast. The floating ruppia at the western end would indicate it was probably dead there too. By then the water level was receding, and the locals believe the rotting rupia  encouraged the growth of the toxic algae.

So where to from here, it appears the authorities are no wiser than they were prior to the near loss of this national icon, they are sticking with their level of 2.5m, though clearly that doesn’t work for the health of the lagoon, the endangered migratory species nor the community of Waituna – all of whom they say is of importance to them.

Points of interest:

  • The earliest known openings of the lagoon were around the turn of the previous century when Maori and farmers/fishermen opened the lagoon by hand. Since 1908 the community has opened the lagoon to the sea, to allow fish passage, farm drainage and enable wading bird habitat. It has been opened when it reached a level of 2m and then more latterly 2.2m so therefore, opened once a year on average. It is this opening which allows the flushing of nutrient and sediment out to sea.
  • Arguably, everyone with an interest in the lagoon has played a part in the degradation of it – either as an individual or as part of a well-meaning organisation. But, it is farming that has always been blamed for the nutrients and sediment which have accumulated in the lagoon, and certainly some has come from farms in modern times, but the degradation of the lagoon started decades ago when the government of the day, back in the 1950s, encouraged development of the district. The straightening of the feeder creeks by the Catchment Board only added to this flow of sediment, although it did lessen the flooding.
  • Prior to the opening of Jan 31, 2024, the lagoon hadn’t been opened since Sept 2021 when it was opened by the Lake Waituna Control Association. It should be noted that the lagoon never turned to an algal dominated state while the Control Assn had consent.
  • ES staff began pressuring the Control Assn to relinquish the consent in 2019. Some land had been purchased by the Whakamana te Waituna Trust and the regional council – that land was bought on the basis of the lagoon level not being above 2.3m. But they did not buy all land affected.
  • The Control Association fought to retain it’s opening consent. This wasn’t a cheap process and the community, and many fishermen and hunters wasted over $90K on this process before eventually withdrawing its application. The continuous rights, held by the Assn, were lost as there was no option to transfer these rights. This meant no-one could now legally open the lagoon, still can’t.
  • Waituna Lagoon is a large part of the 3500ha internationally recognised Awarua Wetland. It was designated a Ramsar Wetland of International Importance in 1976.


– Jo Crack and her family are sheep and dairy farmers who farm directly beside Waituna Lagoon.

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Category: Environment, Waituna

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