Waituna Lagoon is on the receiving end of sediment and nutrient run-off. Photo: Supplied / Sarah Crump
An ecologically significant Southland lagoon that has been plagued by algal blooms and deteriorating water quality is at risk of crossing a tipping point without intervention, the Department of Conservation says.
Waituna Lagoon, south-east of Invercargill, is part of the internationally significant Awarua-Waituna Wetlands - but its position at the bottom of a 20,000ha intensively-farmed catchment area means it is on the receiving end of sediment and nutrient run-off.
An independent panel is considering a consent application by the Southland Regional Council, Te Rūnanga o Awarua and the Department of Conservation (DOC) to determine if the lagoon should continue being periodically opened to the sea to manage water levels.
The council used emergency powers twice last year to open Waituna Lagoon to flush out cyanobacterial bloom.
At the first day of the hearing on Tuesday, DOC solicitor Pene Williams said the lagoon was an ecologically significant site that was home to native birds, fish and plants.
"More than 90 species of birds have been recorded. It is a place where the arctic migratory species come in our summer, their winter. There's also waterfowl, waders, wetlands species. Some of these are at conservation concern," she said.
"It's a place that people go to recreate, including to appreciate its ecological values, and its cultural values. It's the only remaining coastal lagoon on the east coast in a natural ecological condition but it remains at risk of crossing that tipping point without action being taken."
During a public notification period last year, 51 people made submissions, 42 of which opposed the change.
Many submitters sought changes to the frequency or duration of the lagoon openings, raising concerns the proposed higher water levels could cause flooding and impede drainage.
Fish & Game and Forest & Bird objected to a proposed 20-year transition period in the plan, which would involve gradually raising the water level thresholds at which the lagoon could be opened to the sea.
Both organisations wanted higher water levels to begin without delay.
Williams said DOC, the council and Te Rūnanga o Awarua were committed to working with the community to restore the lagoon.
"We have submissions from people who deeply care about Waituna, who have been recreating, working, observing, celebrating Waituna for generations," she said.
"This [plan] is managing the lagoon as the receiving environment for what is coming down the catchment in a way which promotes hauora, and restores it."
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