Lagoon emergency opening could have been avoided

| April 11, 2024 | 0 Comments

As with any issue there needs to be balance and the Waituna Lagoon is no exception, according to Waituna Catchment Group Chairman Maarten Van Rossum.

Recent articles in the media have told only one side of recent happenings in the catchment, which is 40km south-east of Invercargill, in Southland.


November 6, 2023 ES testing shows toxic algae present in Waituna.

January 11, 2024, ES issues a toxic alert for the lagoon. The lagoon was not its usual brackish colour; instead, it was affected by toxic cyanobacteria (algae) and turned a murky green.

January 31, 2024, ES opens the lagoon to the sea under emergency powers. The cool, clean salt water from the sea continued to flush the algae, nutrients and sediment from the lagoon until it pushed up enough pea gravel to end the cleansing process.

Easter 2024, Lagoon closes to the sea.

“The emergency opening didn’t need to happen. If politics had been left out of the scenario, if the previous consent holder had not been opposed by DOC and Iwi, the lagoon would never have turned into an algal dominated state,” Van Rossum said.

The Waituna farmer said the previous consent to open the lagoon to the sea was held by the Lake Waituna Control Association and as part of their consent renewal application they held continuous rights.

“The community advocated hard to keep this running until a new consent was agreed upon which, in the end, was not good enough for the other stakeholders and we were out-resourced.

“The end result was the continuous rights were lost and now no-one can legally open the lagoon to the sea.

“It may have been a simple way the Control Assn managed the lagoon – water levels were the trigger for opening and varied between 2m and 2.2m depending on criteria such as time of year.

“But this also allowed fish passage and ruppia to grow and flourish. There is now none of that.”

Previous to the emergency opening of the lagoon by Environment Southland on 31 January 2024, it had not been opened since September 2021.

“In that time nutrients and sediment had built up in the lagoon, the water had become too deep and the ruppia which does not want to be submerged at 2.3m for more than 20 days had been starved of light and subsequently died.

“The locals believe this dead seagrass then decomposed, adding to the retained nutrient loading and ultimately setting off the algae bloom,” Van Rossum said.

It is well known that nutrients and sediment are the leading cause of the issues at the lagoon. The blame for this has always been laid at the door of the farming community.

“And, there will be nutrients flowing into the lagoon, just like any other area throughout the country, whether that be from a natural or modified catchment.

“The key to unlocking the potential of those nutrients and keeping them on the land is through science and data. If all the data could be publicly made available then all stakeholders could figure out ways to achieve the desired goals.

“Efficiencies across all layers of this issue need to be improved within the organisations who see themselves as guardians of Waituna.

”We also need better communication with them, on any number of levels, particularly in relation to a sustainable way forward for the catchment and for the lagoon.”

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 lately 2.2m so therefore, opened once a year on average. It is this opening which allows the flushing of nutrients and sediment out to sea.
  • The degradation of the lagoon started back in the 1950s when the government of the day encouraged development of the district. The straightening of the feeder creeks by the Catchment Board added to this flow of sediment.
  • Prior to the opening of Jan 31, 2024, the lagoon hadn’t been opened since Sept 2021 when it was opened by the community-based Lake Waituna Control Association. It should be noted 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 was bought by the Whakamana te Waituna Trust and the regional council on the basis of the lagoon level not being above 2.3m. But they did not buy all affected land.
  • The Control Association fought to retain its opening consent. This wasn’t a cheap process as DOC and Iwi were in opposition. The community, and many fishermen and hunters wasted over $90K on this process before eventually withdrawing. The continuous opening rights, held by the Assn, were lost. This meant no-one could 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.
  • The level of 2.3m is significant as the Lagoon Technical Group, a scientific group of coastal lagoon experts, has said 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. The lagoon was over 2.3m for considerably more than 20 days.
  • Other recommendations included regular winter openings to protect the lagoon’s ecology. This appears to have been ignored or overlooked in recent times.

Category: General, News, Waituna

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