Southland Regional Council yesterday announced it would open the Waituna Lagoon to the ocean after toxic algae Cyanobacteria emerged in the area last month.
The council hoped that by opening the body of water, the amount of nutrients fuelling the bloom would reduce and prevent "severe ecological harm".
Doc freshwater and ecosystems threats manager Nicki Atkinson said opening the lagoon was the right move.
"The current state of the Waituna Lagoon is concerning for all involved in the health and management of this internationally significant wetland," Ms Atkinson said.
Doc and the regional council had worked closely with a number of organisations to improve the area, with positive changes observed over the years, she said.
"However, this wetland is extremely vulnerable, and recent monitoring showing extremely high levels of algae make it clear immediate action is needed to prevent permanent harm to the ecological, cultural and recreational values of the lagoon."
In a statement, the council said technical advice received from its science division, the Waituna Lagoon Science Advisory Group, and other independent experts all concurred the lagoon would be worse off if it remained closed.
Mana whenua and Doc had also been consulted with.
The work was being undertaken despite the resource consent — which enabled the opening of the lagoon to the ocean — expiring in 2022.
Instead, the council was using a section of the Resource Management Act 1991 referencing a "sudden event" as justification.
"These powers are not unlimited and must be exercised judiciously," integrated catchment management council general manager Paul Hulse said.
"If they are exercised, there is also a requirement to obtain a retrospective consent."
The Waituna Lagoon was expected to remain open to the ocean for several weeks once heavy machinery had completed the task of connecting it to the ocean.
It had been closed since March 2021 but was opened under a previous consent for many years before that, the council said.
Following the establishment of the Ramsar Convention on Wetlands — an international treaty signed in 1971 — the lagoon and wetlands was among one of the first in the world to be named "a wetland of international significance".
Cyanobacteria can have severe health effects on both humans and animals, and can be fatal. — LDR is local body journalism co-funded by RNZ and NZ On Air
