For years, an invisible line drawn roughly across the Northern Territory below the tiny town of Larrimah has divided the tropical Top End and the arid south, and governed increasingly controversial water entitlements.
But over the past year, environment groups said the NT government had sought to migrate that line north, amounting to what they called "aquifer mining" and "dangerous decision-making".
NT Environment Centre's director Kirsty Howey feared one of the world's most pristine river networks was under threat, as well as sacred sites and tourism gems.
"What we've seen recently is an inexplicable change, that is not precautionary on any reading, to the use of the arid zone rules," she said.
"It's like creating water out of thin air that just was not available for the fracking industry or for other industries that want to get a foothold in the Territory. And it's extremely worrying."
Last year, a massive water licence was overturned by an unprecedented ministerial intervention after it was challenged by the NT's Environment Centre and the Northern Land Council.
It was found the NT Water Controller used the arid zone rules to grant a 10,000-megalitre water allocation to the state government's NT Land Corporation for fruit crops about 500 kilometres south of Darwin, near Larrimah.
The Mataranka Tindall aquifer discharges into the Mataranka thermal springs, stretches south past Larrimah into the Beetaloo Basin, and also keeps the Roper River flowing through the dry season.
It is not governed by a water allocation plan yet, despite years of delays — but had always been regulated by the more conservative Top End rules.
In its simplest terms, the Top End rules allowed 20 per cent of the recharge from an aquifer to be extracted by industries.
And in the southern two-thirds of the NT, the arid zone rules were controversially flipped, so 80 per cent could be taken out.
"What we've seen since that decision, are licences being handed out for irrigated agriculture, but also for fracking, using the arid zone rules," Ms Howey said.
She was concerned the arid zone rules would be applied to the Larrimah zone of the Mataranka Water Allocation Plan Area.
"The scientific inquiry into hydraulic fracturing in the NT … made it very, very clear that the use of the arid zone rules for any extractive industry in the NT, particularly for fracking, was completely unsustainable," Ms Howey said.
"So if we go down the path of using unsustainable rules that are in clear breach of the recommendations of the Pepper inquiry, and the commitment of the NT government to implement those recommendations … all who rely on this groundwater are in real trouble."
Call for community decision-making
Northern Land Council chairman Samuel Bush-Blanasi said the NLC would do everything within its power to ensure "inappropriate" water management and licensing decisions were challenged.
"I have asked the NT government to do the right thing, to sit down and involve our mob in decision-making," he said.
"We want the views of traditional owners and local people to be a part of water licensing decisions.
Des Barritt has spent his life on the pristine Northern Territory rivers, and feared the rule switch could impact his tourism-reliant business — a campground next to the Northern Territory's Mataranka thermal springs.
Water plans carefully monitored, says government
Just days after the landmark overturning, the NT Water Controller handed out another major water licence using the arid zone rules to fracking company Sweetpea, a subsidiary of Tamboran Resources, which planned to explore for gas in the Beetaloo Basin.
In the decision, the water controller said the permit was located in the "transitional zone between the Arid Zone and the Top End boundary" and the department's hydrologist had advised the application of the Arid Zone principle was "appropriate".
Imperial Oil and Gad has also been approved for a licence and three applications are currently being assessed.
Lauren Moss, the Minister for Environment, Climate Change and Water Security, said a water allocation plan for the Mataranka region was set to be handed down next year.
She said plans were developed using "available science" and took into account estimated sustainable yield, climatic conditions, groundwater flow, and varying recharge rates.
"River and spring flow protections are prioritised and monitored," she said.
"Plans also establish the arrangements for trade, and how allocations will be reduced in drier years to protect the environment.
"The water allocation plan for Mataranka will carefully consider the variability of groundwater resources within the area to be covered by the plan.
"Some aquifers exhibit arid zone characteristics while others exhibit Top End characteristics. The allocation planning process will ensure any water allocation correctly reflects and assesses the impact this will have on the resource, and thus inform appropriate allocation levels."
Data used in decision 'highly contested'
Erin O'Donnell from the Centre for Resources, Energy and Environment Law at the University of Melbourne said no matter where they were applied, "the arid zone rules are exploitative".
"The arid zone rules allow you to lower the aquifer by 80 per cent over a 100-year period.
"Groundwater is going to become increasingly important under a climate change future, so we need to be able to manage it sustainably."
She said data the government used to make decisions was "highly contested", and in a worst-case scenario could end up reversing the flow of groundwater and threaten the government's commitment to providing a strategic Aboriginal Water Reserve.
"This is really dangerous decision-making," Dr O'Donnell said.
"The impacts to tourism would be appalling … the impacts to the Roper River as an ecosystem would be catastrophic, to traditional owners and cultural sacred sites, these are irreversible impacts and this is exactly why you have a precautionary approach."
Last year, the Environmental Defenders Office publicly stated it considered "water law and governance in the NT to be among the poorest in the country".
