A lake near the Alpine Fault in Haast is helping to chart the change in New Zealand's freshwater quality.
The Alpine Fault is marked out on satellite images by the western edge of the Southern Alps snowline. Photo: NASA
Scientist Katie Brasell said lakes were largely under-studied but their secrets were now being unlocked.
Ms Brasell, a freshwater scientist at Nelson's Cawthron Institute, said Lake Paringa told a story of large-scale change over the last 1000 years with each Alpine Fault rupture.
Ms Brasell is among more than 300 scientists who have gathered in Nelson for the 50th annual New Zealand Freshwater Sciences Society conference, which started in Nelson today and has Mātauranga Māori (Māori knowledge) as its theme.
She is at the forefront of a nationwide initiative, Lakes380, aimed at revealing the environmental history of the country's lakes.
Ms Brasell's particular focus has been the lake near Haast, and bacterial communities locked in its sediments which reveal how water quality levels have changed over time.
Katie Brasell Photo: RNZ / Tracy Neal
"So the Alpine Fault ruptures roughly every 300 years and we know about five have happened in the last 1000 years.
"They've resulted in large-scale sediment deposition into the lake which would have a big impact on the fish, the plants and everything that lives in there."
Conference convenor Joanne Clapcott said the conference came at a time when interest in the subject had never been more acute or widespread.
Ms Clapcott, also a freshwater scientist at the Cawthron, said all New Zealanders had a role to play in maintaining and improving the quality of freshwater.
She said there was an increasing need for mātauranga Māori to be at the heart of freshwater science and freshwater management.
"It's a unique knowledge system that Māori bring to our community. It's a process of generating knowledge, both traditional and contemporary, so we'd be silly to try and move forward without acknowledging half of who we are."
Ms Clapcott said there was increasing acknowledgement towards making mātauranga part of the conversation.
Joanne Clapcott Photo: RNZ / Tracy Neal
"It's fair to say also there's been an increased focus on fresh water over the last 12 years and a lot of that has come with a growing understanding of the negative impacts we're having - our land use choices and our resource choices."
Ms Clapcott said the available data may not reflect a negative trend - it may show improvements, which contradicted a lot of what people were seeing and how they were feeling about fresh water quality.
She said the conference aimed to find solutions to challenges around degradation of fresh water. She said the pressure points were linked largely to climate change.
"I think it's easy to ignore but we really have to be very proactive.
"With a changing climate we all have to think about how that's going to affect our water resources."
Ms Brasell is among speakers at a free public lecture at Nelson's Rutherford Hotel on Wednesday night. Other speakers will address topics such as the role of rivers in transporting plastic debris to the ocean and New Zealand's taonga freshwater fish species.