Researchers behind the largest ever study into New Zealand lakes say it's not too late to turn things around.
However, for many lakes it will take generations and even hundreds of years to see their health improve.
The Lakes 380 project led by the Cawthron Institute and GNS Science found almost half of lakes are in poor health or worse.
Cawthron Institute fresh water scientist Sean Waters says lakes are particularly challenging to restore.
"So lake restoration is really problematic and tends to play out over a long timeframe," he said.
"And part of that is because nutrients that come into the lake from the catchments get stored in the sediments."
Unlike rivers where water is constantly moving, lakes are largely stagnant making it difficult for changes to happen. Plus each lake has unique problems that can take generations to be solved.
Lakes380 researcher Riki Ellison said the data confirms what many Māori had long suspected.
"It's sad and it's frustrating the state of a lot of our environment. The fact that some places we can't access them or we can't collect kai there.
"It's an obligation we can't avoid as kaitiaki to fix those things."
The researchers behind Lakes380 said there needs to be more restoration solutions and better monitoring. Currently less than 5% of New Zealand lakes are checked regularly.
Environment Minister David Parker said monitoring was usually done by regional councils, but it wasn't perfect.
"One of the challenges we have is that we don't have standardised methods of monitoring and so we need to do better as a country in terms of combining up with ways we do that.
"I think regional councils want to cooperate with central government in that regard, we don't necessarily need to have to wave a big stick to do that."
Victoria University ecologist Mike Joy says stopping intensive farming would have the biggest impact on lake health.
"There's a whole lot of actions you could take but actually just switching off the taps, stopping the nutrient supply is the first step and then ecosystems are pretty good at repairing themselves if we give them a chance."
Cawthron Institute fresh water scientist Susie Wood said the Lakes380 project had allowed them to develop a simpler way of figuring out what's below the surface.
"So all organisms shed DNA into the water and the environment around them. And we can design methods to go and detect those species that are super sensitive and specific."
It essentially means they can take same samples of water of soil and test it for the DNA of certain fish or organisms.
"So it really saves us with getting out there with big surveys and divers," Wood said. "We can actually really quickly now determine what lives in a lake."
Innovation or new ways of restoring lake health is a focus for researchers too.
Sean Waters says there is a natural material to try and keep oxygen on the lake floor, which would help prevent algae and poor water quality.
It's called nano bubble technology and if it's successful would be a world-first.
Waters said it's important to have lots of tools in the toolkit.
"If we think long term and bring communities on board then I think we can bring most of our lakes back to good health."
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