Up close, after it has travelled more than 300km, the Waikato River is so muddy that you cannot see your feet if you are standing just knee-deep beside its banks.
Above the current, on a concrete pier that juts into the river, Asaeli Tulagi hauls a metal cylinder from the water. Padlocked inside the tube is a $25,000 recording device which gathers and stores information about the health of the river.
Tulagi, a technical specialist with the Waikato Regional Council, replaces the instrument, known as a datasonde, with a freshly-charged recorder which he lowers into the flow.
"We're building a picture of the river," says Tulagi, who started this morning sampling the river at Hamilton. His recovery of the sonde is the last of six stops along the lower Waikato on a bend in the channel known as the Elbow. "We want the best possible information because the river is the lifeblood of the region."
At the point where Tulagi collects his samples, data gathered on many earlier trips offers a snapshot of the river as it nears the end of its journey. It shows that bacteria levels are borderline, which means, were it warmer, it would not be a good idea to swim in its turbid current.
Besides e-coli, the river water contains traces of nitrogen, phosphorous, boron and, because far upstream the Waikato crosses geothermal areas, measurable amounts of arsenic. Not far from where Tulagi completes his work, a fat pipe sucks water from the top of the flow into a treatment plant where its is stripped of all the nasties and pumped to households in Auckland.
Sometime in the not-so-distant future, Watercare, the company that runs the $150 million plant and pipeline, expects it will need to double the capacity of the pipe feeding its state-of-the-art Tuakau complex and draw a lot more brown water from the great river to satisfy the demands of an extra million people in Auckland. Except it may not get its hands on the water it needs, at least not easily and not without lawyers being involved.
The Waikato, for all its placid appearance, has once more become a source of tension between competing users as power generators, irrigators, industry and drinking water suppliers such as Watercare press their case for a share of the river. Before Watercare can divert more of the Waikato's flow that it needs to feed to a rapidly growing city, other powerful river interests want to satisfy their own requirements.
The battle will almost certainly end up in court, as lawyers argue over a draft plan which carries as many currents as the river itself. The blueprint is meant to allocate water among rival users, nurse the river back to health and ensure its wellbeing for years to come.
A sign the plan - the proposed Waikato Regional Policy Statement (RPS) - faces turbulent times lies in the fact that 37 appeals have been lodged against it. None yet has a date before the Environment Court, as conversations have started between the parties and the Waikato Regional Council, the agency that drew up the document and looks after what is one of the most complex and challenging stretches of water in the country.
The language in some of the appeals hints at the battles to come. Mighty River Power - whose fortunes rest on the river - pressed its case to have priority in the water allocation stakes with its view that the proposed RPS "lack of recognition" of the Waikato Hydro Scheme was a "profound and inexplicable shortcoming".
It continued: "This shortcoming has the potential to adversely impact on the existing and continued operation of the scheme and on this occasion has resulted in the development of unrealistic and inappropriate objectives and outcomes for future regional and district plans."
Stripped of the legalese, Mighty River - now partly privatised and listed on the NZX - is arguing that the council's draft policy could be costly for its massive Waikato hydro assets, which produce 8 per cent to 9 per cent of New Zealand's electricity needs. The power giant is also unhappy that the draft, as its stands, could compromise its future plans and wants the council's statement amended to strike a balance that Mighty River considers is missing from the document.
Mighty River argues its guaranteed access to water needs higher priority that the council has given it, and wants the water taken for towns and cities "closely scrutinised."
It says its power plants and lakes from Taupo to Karapiro have modified the river itself and "shaped the historic development of the region" and the RPS "needs to recognise that the options for management and health and wellbeing of the Waikato River will be circumscribed by the practical implications of the Waikato Hydro Scheme's existence and continued operation".
Asked about its submission, a Mighty River spokeswoman replied: "While the review is under way we do not wish to make any further comment, except to say that we support the vision for a healthy and well-managed river and have confidence in the review process. We continue to work closely with WRC - alongside the other 36 submitters - to ensure an outcome that accurately represents the views of the wider community."
Mighty River is not the only generator with power plants on the river. Genesis owns the imposing Huntly thermal power station, which uses the river to cool its separate plants. Contact Energy has geothermal plants at Taupo. They also have misgivings about the RPS and have lodged appeals.
Whereas Contact and Mighty River's interests lie in the upper stretches of the Waikato, Watercare is a bottom-end user. Its appeal against the RPS reflects the reality that its thirst for future water comes a long way down the list, even though municipal water suppliers are accorded priority status.
New applicants have been lined up for some time ahead of Watercare for a share in available Waikato flow, meaning Auckland's water company will get an assured supply only if a permit holder gives up its consented take, more water becomes available or if the regional council decides not to renew consents when they expire at the usual term of 10 years.
Watercare explains its dilemma in these terms: "None of these possibilities provide the efficiency and certainty that is desirable to ensure the continued wellbeing of urban communities. When full allocation is reached, urban communities will be forced to compete with rural communities for water resources."
The water supplier's solution to its dilemma is for the regional council to ensure municipal needs get to the top of the consent queue - a solution that puts it into conflict with Mighty River.
So how can these contests be resolved?
Opposing sides in the water disputes would, they say, prefer to reach settlements away from the court. Watercare says it has had one meeting with WRC officials "and we expect these meetings to continue".
This is music to the ears of Dr Ed Brown, acting water allocation manager at the regional council. Brown, a hydrologist, expects that within five or so years there won't be any more Waikato water to share around.
That's because the council - or rather the Environment Court, after a nine-week hearing in 2011 during which 68 witnesses gave evidence - set a limit on the amount of Waikato water available for users to take, in a decision over a council project called Variation 6.
Essentially this is a fiercely-contested set of rules to deal with competing demands and sustain the long-term health of the Waikato. Nearly a decade in framing, Variation 6 is the holy grail for Waikato water and is designed to strike a balance between users who depend on the river for their business and the need to protect aquatic life. Take too much out, and the river suffers as its loses its life-nourishing oxygen.
The court increased the amount the council was prepared to allocate, striking a limit of 5 per cent of a five-year average of the river's minimum flow at Karapiro dam. With industrial water users, the council wants to encourage storage to reduce peak demand, upgrading of equipment which requires less water, recycling where possible and investigating trading water from one user to another if their heaviest demands do not coincide.
Says Brown: "Eventually there won't be enough. We'll reach the allocation limit in the next five or so years, and that's what we've been planning around in the development of our rules."
He accepts there will be conflict among rivals wanting to increase their take from the river. Pressure on Waikato water has ramped up in recent years, especially with the expansion of dairying and the need for irrigated pastures. With that has come extra demands for water to hose down dairy sheds and for stock to drink. "There is not enough to go round for everybody who wants it for their purpose," he says. "If you allocate a drop of water at Lake Taupo, then it is not available at Tuakau."
The council is guided by the Resource Management Act in its consent decisions, partly on a first-come, first-served basis, a policy that trumps the preferential consent status of municipal users. Observes Brown: "If it's all applied for by one sector, then so be it. We cannot run a beauty parade and look at consents the way some argue they should be. So if, for instance, horticulture or pastoral irrigation applies first and they meet the tests of our plan that there's sufficient water [and] there's no impact on the environment, then they would be allocated water."
He accepts the council faces demands to allocate more river water, but that approach has the potential to compromise its equally pressing requirement to guard river quality.
"If we were to increase the allocation, then we have to assess the effect on the overarching purpose of the vision and strategy which is to restore and protect the health of the river. We know that for every drop of water you remove you generally get a decline in quality," Brown says..
"Basically the biggest constraint on us allocating more water is the quality and ecology of the river."
He adds: "We're not going to change our viewpoint too much. That debate really has just been had in the court [the Variation 6 battle] ... all the top planners, the top lawyers were there."
Brown considers the council is on firm ground with its approach. "Once you start tweaking one part then you throw it out of balance. We don't want to reopen a can of worms."
A river runs through it
The Waikato is New Zealand's longest river. Starting at Lake Taupo, it runs 425km to the Tasman Sea at Port Waikato. The next longest (322km) is the Clutha, which drains Lake Wanaka.
The catchment runs up Mt Ruapehu's eastern flanks but the river itself begins where it empties Taupo before crashing over Huka Falls. As it flows north and out to the West Coast, the river runs through farms, towns and Hamilton, surges over rapids, fills lakes behind eight dams and spins turbines at nine hydro stations that produce electricity for the national grid. Before the dams were built, it took six days for a drop of water to reach the sea from Lake Taupo. Now it takes a month.
Every drop that flows down the river is calculated to be used at least seven times, mostly by passing through the power plants. Once one of the country's most polluted waterways, dirtied by raw sewage, industrial waste and abattoir effluent, the Waikato for much of its length is today in much better shape.
At its origins the water is clear and clean. Below Ngaruawahia, where the muddy Waipa River joins the Waikato, water quality dips and is either borderline or below Ministry of Health guidelines for swimming. Under the Waikato-Tainui Treaty settlement, $210 million was set aside in a contestable fund to restore the health of the river over 30 years. The Waikato River Authority administers the fund, part of a broader "vision and strategy". One of its objectives is to restore quality so that the Waikato - which means "flowing water" - is safe to take food from and swim in over its length.