A new survey of Waituna Lagoon in Southland shows a significant improvement in health for the internationally important Ramsar wetland compared to a year ago.
The good news coincides with the celebration of World Wetlands Day (2 February), marking the signing of the Ramsar Convention on Wetlands – a global treaty to conserve and sustainably manage all wetlands, including lakes, rivers and estuaries.
Waituna Lagoon is one of 2,520 wetlands around the world recognised as internationally important for its outstanding biodiversity values. This Ramsar site is one of the best remaining examples of a coastal lagoon in New Zealand and supports many threatened species such as Australasian bitterns and longfin eels.
Department of Conservation (DOC) River Ranger Pat Hoffmann says the results of lagoon's annual survey last summer showed it failed to meet any of the ecological targets
"The aquatic plants that help stabilise sediment, improve water quality and provide habitat for fish were in low numbers. At that time, the survey was conducted when the lagoon was open to the sea.
"This year, DOC and Earth Sciences New Zealand carried out the survey when the lagoon had been closed for nine months so we were curious to see the results. As it turned out, the results were better than we could have expected.
"Our monitoring across 47 Waituna Lagoon sites showed most parts of the lagoon had very little algae – an indicator of poor water quality. This is terrific given the lagoon experienced an algal bloom in 2024. However, researchers note that algae abundance can increase quickly when there's high water temperatures and calm conditions, so it's always a risk.
"Most importantly, 80 per cent of monitoring sites had the aquatic plant Ruppia present compared to 36 per cent last year. The presence and abundance of this native species is a sign of good wetland health.
"Another native species that signals a healthy freshwater ecosystem – stonewort – was also thriving. It was found in 54 per cent of sites compared to 7 per cent last year," Pat Hoffman says.
DOC Principal Science Advisor and Chair of the Ramsar Convention's global science panel Hugh Robertson says going forward, the management of both water levels and water quality will remain vital to the long-term conservation of Waituna Lagoon.
"The monitoring helps guide DOC, local iwi and other agencies efforts to look after the sensitive lagoon ecosystem. Many of New Zealand's coastal lakes and lagoons are under pressure, but the survey highlights how nature will respond in favourable conditions."
DOC, Environment Southland and Awarua Rūnaka use this data as part of ongoing efforts to conserve and restore the Waituna Lagoon Ramsar site as a taonga, for its unique biodiversity and as an important naturing site for the local community.
Background information
The Awarua-Waituna Wetlands are New Zealand's first internationally recognised wetland system under the Ramsar Convention on Wetlands, with an exceptional variety of plants and animals and extensive peatlands that store carbon. The wetlands are of great importance to Ngāi Tahu due to their long relationship with the area and wetland taonga species. The area is popular with recreational hunters and fishers.
Waituna Lagoon is a part of the wider Awarua-Waituna Wetlands and is naturally closed by a gravel barrier. An application for resource consent is in progress, to allow it to be mechanically opened to the sea, based on criteria including water level, biosecurity, ecological, water quality, and fish passage.
DOC oversees the monitoring of Ruppia and other aquatic plants and algae to determine the ecological health of the Waituna Lagoon. Six ecological targets are evaluated, such as Ruppia reproductive success.
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