Te Waikoropupū Springs are the largest cold water springs in the Southern Hemisphere and attract tens of thousands of tourists every year.
Nestled in farmland in Golden Bay, and with next-to-no impurities in the water to hide the brilliant green and blues of what lies beneath, the springs look almost like the iris of an eye.
While it's some of the clearest water ever measured, it may not be for much longer.
Talking to Newshub, Save Our Springs campaigner Kevin Moran is anxious about the spring's future.
"We could lose the waters, that's the very worst scenario," he said.
He features heavily in The Unseen, a new documentary by environmentalist Geoff Reid.
The feature highlights the impact nitrate used by farmers is having on Te Waikoropupū Springs.
Nitrate is used by farmers to stimulate grass growth and the grass is then consumed by cattle. The excess nitrogen is either absorbed by the cow as protein, or urinated out onto the soil.
The Unseen focuses on what happens next.
"Nitrate either washes over the ground into waterways, or leaches into the ground or enters the aquifer. The more cows urinating on the paddocks, the more nitrate in the springs," said Reid.
Nitrate concentration in Te Waikoropupū Springs has doubled since the '70s.
Tiny shrimp-like organisms, which keep the water clear as glass by eating the organic matter in the water, are struggling to survive the bump in nitrate levels.
"The amount of animals we've got on the land, the nitrates, the pee patches, and particularly the mud farming... this is really driving up the pollution in the aquifer and it's showing up in the springs. It's causing algal blooms," Reid told Newshub.
After years of court action the Ministry for the Environment issued a Water Conservation Order for Te Waikoropupū Springs in October last year, warning the spring is at a "tipping point".
It said nitrate is of particular concern.
"Despite farmers' stewardship, an increase in irrigation within the catchment since 2005 has corresponded with an increase in nitrate concentrations in the springs," they said.
Corrigan Sowman represents a group of dairy farmers in the catchment and said local farmers are taking the advice on board.
"Te Waikoropupū Springs are a taonga in our community and a taonga for New Zealand.
"Members in our group are fully supportive of looking at new technologies and new information. Right now, it's all about farmers learning from other farmers to be better."
Kerry Cleland has almost entirely removed excess nitrogen from his dairy farm of 360 cows by using regenerative farming techniques and he said others must follow suit.
"They've got such a noose around their necks, some of these farmers, from all the advice they've got in the past and somehow that noose has got to be loosened.
"We don't use any synthetic chemicals on our soil, and the craziest thing about it is, it's extremely profitable."
Maybe that could tempt some farmers into a win-win for them and the springs.
Moran said if not, the spring is in peril.
"It's not invincible, the aquifer. It can't just go on and on and on with excessive nitrate being poured into it."
