Sixteen years ago, when I first vis­ited Pupu Springs, the springs were privately owned, and were little more than a local picnic spot. Wading cows grazed on watercress around the fringe, treating my presence with nonchalant stares as they chewed their green, dripping cud.

I had sought out the place because Pupu, or, more correctly, Waikoropupu, Springs are New Zealand’s largest freshwater springs. (Golden Bay residents may boast, but the springs are down at around 90th place in world ranking. The source of the Manavgat in southern Turkey surges out at a phenomenal 130 cubic metres a second, nine times the average out­flow of Pupu.)

I was prepared to be suit­ably awestruck by this indigenous scene of upwelling power, but, strangely, size left few lasting impressions. I was overcome by simply the most beautiful freshwater en­vironment I have ever seen: a submerged Garden of Eden. I resolved to return and explore its inner world.

I chose a time when I knew I would have the springs to myself. It was a crisp, cloudless mid-winter day as I struggled with my wetsuit, nowadays one ego-deflating size too small.

Immediate stabs of cold jolted me as I dropped into this enchanted realm, but were as quickly eclipsed by the scene before me. Shades of tur­quoise and azure blue provided the backdrop for a spectacular array of aquatic flora. A rumpled carpet of mosses, algae and liverworts encrusted the stony bottom, while stands of higher plants, including milfoil, duckweed, pondweed and submerged cress, swayed in the aquatic “breeze”.

I found the main vent, some five metres deep, and tried to imagine the subterranean labyrinth of marble tun­nels and caverns which forms the springs’ immediate source. While nearby stones jostled and rattled I watched the upthrust of water which has spent up to ten years under­ground surge its way to the surface.

The total flow of Pupu Springs ranges from 7 to 21 cubic metres per second, with an average flow of around 14—the equivalent of 40 do­mestic bathfuls of water bubbling out of the ground each second. In the Main Spring a sweeping canyon containing eight vents provides most of the input. A few metres away, the Dancing Sands vent offers a delicate granular ballet as further water discharges through sand.

Since the turn of the century, Pupu Springs have belonged to the Campbell family. Before that they were sacred to the Maori, who gave them the name Waikoropupu, mean­ing “bubbling waters”. In 1979, the springs were bought by the govern­ment, and they are now adminis­tered, in a low key but effective man­ner, by the Department of Conserva­tion. During the holiday season over 400 visitors a day amble along boardwalks and gravel pathways, winding their way through old gold workings and regenerating bush be­fore reaching the Main Spring.

Above-water visitors, or “passive users” as DOC refers to them, have had little effect on the springs since they became a popular picnic spot as early as 1880. But an increasing trend towards “active users” has many people worried. The springs’ growing reputation as a stunning freshwater dive has meant that more adventurous visi­tors are now bringing their wetsuits and diving gear along. A 1980 estimate put divers at just one a week. That yearly total of 50 or so is now exceeded in just one day in summer.

A conflict of interest is brewing. Passive users come to admire from above, and divers from below. There is no doubt that some visitors are fascinated by the divers swimming around in front of the observation stand. But there are many who believe that this activity violates the peaceful serenity of the place and ultimately, if it goes un­checked, threatens the springs themselves.

Flippers dislodge particles that affect the clarity of the water. Many divers disturb vegetation in their meanderings around the shallow fringe. With weights it is possible to descend beside the main vent—liter­ally a blast of an experience—but this, too, creates problems as divers grab hold of rocks to try and resist the upthrust.

The issue of divers is a tricky one. Concession applications for dive tours, glass-bottomed boats, under­water viewing scopes, even a shantytown, have all been turned down by DOC. “No commercialisa­tion” is the verdict. The rules are slightly different downstream. A wa­ter right to take and discharge four cubic metres a second from the  Waikoropupu River was granted to the Bubbling Springs Salmon Farm (now Southern Ocean Salmon) in 1985. The intake is just downstream from the springs.

Divers were initially concerned that the taking of this water would affect their drift diving, especially in summer when water levels are at their lowest. It is true, the odd belly rub in shallow water does interrupt the floating joyride downstream to the Pupu Bridge. But now the salmon farm is asking questions back. Questions about what effect the divers are having on the purity of “their” water. Large clumps of dis­lodged algae are a nuisance to the farm, and even the issue of urine contamination is raised. Cold does have that effect!

Here is the complicated part. Sce­nic reserves are administered by DOC in accordance with the Re­serves Act 1977. The springs’ aquatic flora and fauna are protected under this Act. But the subject of water conservation and its use comes under the auspices of the Tasman District Council, which ad­ministers the Water and Soil Conser­vation Act 1967. Ironically, Pupu water itself is not protected, even though it provides a habitat for the protected flora and fauna. While it has been relatively easy for DOC to curb commercial interest in the springs, the problem of increasing numbers of freedom divers remains unresolved.

The question of where Pupu Springs water comes from has exer­cised the minds of scientists for close to 100 years. Traditionally, the upper Takaka River has been re­garded as the prime contributor. Dur­ing summer, this not inconsiderable river commonly runs dry in its gravelly bed at a point about 16km inland from the sea—even though its headwaters may still be flowing at a rate of several cubic metres a second.

To understand how a river can disappear into the earth you need to know a little chemistry. During its passage through the atmosphere, rain dissolves carbon dioxide to pro­duce a weak solution of carbonic acid, which can dissolve limestone and marble rocks. (Put vinegar—a slightly stronger acid—on a piece of limestone and you will see a more dramatic demonstration of the same effect.) Over the eons, water has lit­erally excavated huge drainpipes through the marble that underlies much of the Takaka Valley.

Fifteen million years ago, when the local area was thrust up out of the sea for the last time, faults in the predominant rock type, Mount Arthur marble, caused zones of crushing and shearing which al­lowed water to penetrate the rocks and slowly form a system of caves in the marble.

In the upper part of the valley the rocks leading into this cave system are exposed, and the rivers and streams which traverse the terrain and drain the surrounding moun­tains lose water to the underground aquifer.

Over the lower part of the Takaka Valley, towards the coast, an overly­ing layer of coal-bearing rock and mudstone acts as a tight lid on the aquifer-bearing marble, preventing water from escaping. Silt deposition at the mouth of the Takaka River puts extra weight on to the lid, pressurising the system. At Pupu, a fault combined with an area of very thin cap allows water from the aquifer to burst out, creating the springs.

Fish Creek Spring, 130m from the Main Spring, but three metres higher, acts as an overflow for the Pupu system. Its flow ranges from zero in dry periods to as high as eight cubic metres per second after flooding. Three offshore vents in the sea-bed provide additional outlets.

Proof that the Takaka River was contributing its flow to Pupu Springs has only come in the last two decades. Conventional tracing dyes could not be employed in such a large system, since, by the time it emerged, the dye would have be­come too diluted to detect. A new method was used by Paul Williams, an Auckland geographer, in 1975, to establish the Takaka River link. “Pulse train analysis” uses the prin­ciple that an input pulse, such as a flood wave, will transmit itself as a pressure wave which can be moni­tored when it emerges.

The Electricity Department co­operated in the experiment by releas­ing small flood waves from the Cobb Dam, high in the hills behind Takaka, at prearranged intervals. The main pulse travelled down stream as a distinct wave front be­fore disappearing underground and finally being recorded at the springs 15 hours later.

This does not mean that Takaka River water entering the under­ground reservoir would spend just 15 hours before emerging. Consider a hose full of water. You turn on the tap for a second, and water will squirt out the other end of the hose—but it is not the water that the tap just put in. Tritium analysis has shown that Pupu Springs water has been underground for an average of three to four years, and possibly as long as a decade. This gives it plenty  of time to cool down and emerge at a constant chilling 11.7°C.

­

Two other characteristics of the springs are still open to speculation: their tidal nature and slight salti­ness. The tides are small—only 4mm at the Main Spring and 16mm at Fish Creek Spring. The hours of high and low water precede nearby Golden Bay by roughly an hour, but the fact that every second tide is twice as high is suggestive of earth tides rather than marine tides. (Earth tides result from the flexing of the earth rather than the movement of the seas. When sun and moon are aligned, the gravitational pull is suf­ficient to distort the earth’s shape, and this distortion can be detected as “tides” in large bodies of water. It is quite possible that the 1.5 cubic kilometre underground reservoir at Pupu Springs is showing this effect.)

It was initially thought that the slight brackishness of Pupu water arose from back-flow through the marine vents, but it is also possible that dense seawater penetrates the flooded cave system under Takaka Valley. Caught up in freshwater cur­rents, it mixes by a venturi process to finally contaminate the springs. Only a small amount, though—one part in 200, or 0.5 per cent.

Although officially “discovered” in 1957 by the hydrographic survey ship Lachlan, the three offshore freshwater springs had been known to Golden Bay fishermen for years. They can be felt as boats cross over them, and in calm conditions the upwelling can be clearly seen on the surface.

These submarine springs lie some 10km from Pupu Springs, at depths of 13 to 15 metres. One is halfway between Tata Islands and Taupo Point, one is due north from Tarakohe and the third, most off­shore, vent is 5km northeast of Waitapu.

Pure water has become an impor­tant commodity in an increasingly polluted world. Not surprisingly, en­trepreneurs have seen opportunities for exporting bottled water in the Pupu system. A spate of water ab­straction applications in the 1980s (including one which would have seen a barge moored permanently over one of the marine vents) prompted a deeper understanding of the springs’ hydrology, just as div­ing activity in the 1990s will prompt discussion on turbidity and ecologi­cal fragility. All abstraction propos­als have so far been turned down; the only commercial use of Pupu water involves diversion, rather than removal, of the water.

The salmon farm’s water right, granted after a lengthy series of hear­ings before a special tribunal, allows it to divert water from the Springs River, use it as the growing medium for its fish, then return it to the river. Fish food and faeces are removed by sludging, and stringent monitoring of the discharge has shown only “a slight decline in stream health” downstream.

One form of extraction from the springs that the Department of Con­servation has allowed is the removal not of water, but of watercress.

The springs’ purity, constant tem­perature, high calcium content, strong current, depth and size all contribute to a luxuriant cress growth that is found in no other lo­cation in New Zealand.

Watercress (Nasturtium micro­phyllum) was introduced to New Zealand from England around 1850, and spread rapidly to become com­mon in slow, shallow streams and cold springs throughout the country. It has been a real problem in the Pupu, at one time covering nearly a fifth of the Main Spring, and the Dancing Sands completely.

Nigel Mountfort, a DOC officer in Takaka, has probably had more to do with the springs, and the watercress, than anyone else. He explains: “When we purchased the springs in 1979 the first thing we did was put in a secure boundary fence to keep stock out of the new reserve. Cows had been regular munchers in the springs, wading out on the fringes to get the tasty cress. Suddenly we had a problem. And it wasn’t confined to the water; cress was even found growing two metres up trees around the edge.”

DOC declared war with a simple but tedious strategy: manually pull it out. Years of effort have finally brought the weed under control, but Nigel, who refers to watercress as Old Man’s Beard of the Deep, warns “absolute vigilance is still required on this front”.

Cress in the springs has both an emergent and submerged form, and can be found both rooted and float­ing. Elsewhere, cress does not grow in water deeper than a metre, but at Pupu it grows as deep as 6.5 metres. These plants get a reduced amount of sunlight, are usually smaller and resemble the “winter” form through­out the whole year. Possibly the world’s deepest watercress, these plants attest to the remarkable grow­ing properties of Pupu water.

Deja Kjoller and Keith Orr call themselves “Springfresh Watercress” and operate under the only DOC­ granted concession within the Pupu Scenic Reserve. Their permit allows them to harvest a modest 50kg of wa­tercress weekly from the Springs River during the cooler winter months— an arrangement DOC sees as mutually beneficial.

I caught up with the two pickers mid-river amidst a lush, low-lying archipelago of watercress. Wading behind in the swift current, I fol­lowed their backbending manual task until all the sacks bulged with dripping cress. Deja held up a vital-looking sprig, vivid green and free of any blemishes. “It’s the best around, completely free from disease and liverfluke. Highly nutritious, it’s probably the best value winter veg­etable you can buy on the supermar­ket shelf.”

For many people, though, the gathering provides as much enjoy­ment as the eating. Recognising this, DOC has set aside a small area of watercress at the confluence of Fish Creek for the public to help them­selves. And it is superb, just by itself or in a salad with dressing. For me, a trip to the springs just isn’t complete without that crisp peppery taste.

“A wise man . . . enjoys the purity of water,” said 14th century Zen master Muso Soseki. In the last 10 years, appreciation for the springs has grown to the extent that they are now Golden Bay’s number one tour­ist attraction. But without protection of the water itself, a threat of pollu­tion or physical damage hangs over the site. A national water conserva­tion order would not only recognise Pupu’s national importance, but would provide protection from wa­ter extraction in the lower Takaka catchment which might eventually harm this unique site.