Environment Southland will use emergency works powers available to it under the Resource Management Act to mechanically open the Waituna Lagoon to the ocean with the aim of preventing imminent, severe ecological harm.
Urgent management action is required to disrupt a toxic algal bloom (cyanobacteria) which emerged in the lagoon last month, and to reduce the amount of nutrients within the Lagoon fuelling the algal bloom.
Technical advice received from Environment Southland’s Science Division, the Waituna Lagoon Science Advisory Group and other independent experts, all concurs that the lagoon is currently experiencing adverse environmental effects and the situation is likely to be further adversely affected if it remains closed. Monitoring has identified that there is a risk to ecosystem health if the Lagoon remains closed, with the latest samples showing toxic algal bloom levels higher than any recorded previously.
Following consultation with mana whenua and the Department of Conservation, and weighing of environmental and health and safety risks, it has been agreed that work will be commenced this week to open the lagoon.
Environment Southland’s General Manager Integrated Catchment Management, Paul Hulse, said Environment Southland is the entity with jurisdiction over the Waituna Lagoon but no person holds a current resource consent to enable the opening of the Lagoon, given that the previous resource consent expired in 2022.
However, Section 330 of the Resource Management Act 1991 provides various emergency powers in certain circumstances. An important consideration under Section 330 is whether there is an element of immediacy. Section 330(1) references a “sudden event” and / or “immediate” preventative or remedial measures.
“These powers are not unlimited and must be exercised judiciously. If they are exercised, there is also a requirement to obtain a retrospective consent,” Mr Hulse said.
The most suitable method available to achieve this is to mechanically open the lagoon to the ocean, and to ensure it stays opened for long enough. This would typically be for several weeks, unless a shorter closure is followed by immediate filling of freshwater that is ideally low in nutrients.
The physical opening will require the use of heavy machinery and the public are encouraged to stay clear of the area of the works, which will be advised before the work starts.
“While there is some uncertainty as to how effective this opening will be, our belief, which is supported by interagency science opinion, and which recognises mana whenua and local community concerns, is that it is appropriate for us to take this action to seek to mitigate adverse effects on this internationally significant area,” Mr Hulse said.
The Waituna Lagoon has been closed to the sea since 2020 but was periodically opened under a previous consent for many years before that. While such a closure can have ecological benefits in terms of certain organisms that are important for Lagoon health, long periods of closure result in reduced flushing of nutrients.
Waituna Lagoon and wetlands were among the first sites in the world to be named “a wetland of international significance” under the Ramsar Convention on Wetlands, an intergovernmental treaty signed in in 1971.
The area is an important habitat for birds, fish and eels and is home to some unusual plant species. The lagoon is also a significant trout fishery and a popular walking area.