Lagoon Management
Lagoon management update - March 2025
The Lagoon has remained open since September 2024, following significant rainfall and high water levels.
Section 330 of the Resource Management Act allows for undertaking ‘emergency works’ (to mechanically open the lagoon) if any of the following apply:
- an adverse effect on the environment which requires immediate preventive measures; or
- an adverse effect on the environment which requires immediate remedial measures; or
- any sudden event causing or likely to cause loss of life, injury, or serious damage to property
When emergency works might be actioned
The following are some scenarios/triggers when Environment Southland would assess the situation against the 330 criteria, and consider the use of emergency works.
Considerations
- Three years have passed since the Waituna Lagoon was last opened (either naturally or artificially). If ecological advice demonstrated risk to biodiversity, an opening to take immediate preventative measures to avoid that effect may be justified.
- An extensive bloom of algae or cyanobacteria that may have wider, adverse ecological impacts.
- The sediment build-up or changes to the sediment composition that was so significant it posed a threat to the ecological health of the lagoon.
- One or more nutrients reach critical levels whereby there is an increased risk to the severity of algal blooms or water chemistry becomes harmful or toxic.
- Ruppia density exceeds and is having an adverse effect on the ecological and cultural health of the lagoon.
- Dissolved oxygen saturation reaches levels that pose a threat to the ecological health of the lagoon. This may be super-saturation or hypoxic/anoxic.
- If the forecast water level is likely to cause ongoing serious damage to critical property or infrastructure
Consideration would also be given to the safety of any potential opening before any action was taken. Consideration will also be given to the potential ecological effects of an opening, including the duration it will remain open.
Each situation must be considered on a case by case basis. Reaching a trigger level does not guarantee any action will be taken. Any decision will also take into consideration the longer term effects of opening the lagoon, and timing.
Waituna Lagoon opening consent application
The existing permits that provide for openings of Waituna Lagoon expired in early 2022.
Te Rūnanga o Awarua, Department of Conservation and Environment Southland are joint applicants for a new resource consent to open the Lagoon. The primary purpose of the application is to establish a new opening regime focused on the ecological health and cultural values of Waituna Lagoon.
A pre-hearing meeting for the application is scheduled for 7 March 2025.
Waituna Lagoon opening background
Waituna Lagoon has been periodically opened to the sea by artificial means since 1908. The initial openings were to aid game fish passage and since 1958 the primary purpose of the openings has been to aid land drainage. Lake openings also enable the flushing of nutrients and sediment and aid native fish passage. The Lake has generally been opened about once a year, usually when the lake level gets to 2m above sea level. The existing permits (in place until decisions are made about the opening consent) include resource consent conditions that determine when the Lake can be opened at different times of year, including specific water levels.
View the existing (pre-2022) coastal permit.
Ongoing work on to improve the ecological health of Waituna Lagoon and its catchment led to the formation of the Whakamana te Waituna Charitable Trust. The Trust has implemented a number of initiatives including a programme of work within the Waituna catchment focused on improving the health of the lagoon and ensuring the rural community thrives. Part of this work programme has focused on relieving the pressure on farm land from high lagoon levels by creating a landward buffer.
In 2020/21, the Trust initiated a workstream to develop an opening regime for the Waituna Lagoon that supports ecological health and cultural values. This involved reviewing the current consent conditions and considering a broad range of ecological and cultural values associated with the lagoon. A Technical Assessment has been prepared that assesses the effects of openings and makes recommendations on a new opening regime based on ecological and cultural values. The Technical Assessment recommends an opening level of 2.5 metres as well as provisions to open the lagoon to facilitate fish passage and for flushing excessive nutrients.