If you want to realise how far the water level has fallen, it is worth stopping on Route 90, not much more than a kilometre south of Qumran where a Bedouin looking for a lost goat discovered the first Dead Sea Scroll in a cave in 1947.
The shimmering expanse of the sea, stretching east to the Jordanian cliffs, is obscured here by reeds and shrubbery that have grown up around the freshwater spring of Ein Feshka. So look up at the cliffs lining the road on the western side, formed from limestone deposits perhaps 80 million years old. About 12ft up, you can see a red line less than a foot long. It was painted on the rock just over 100 years ago by members of the Palestinian Exploration Fund, a venerable British institution which counted T E Lawrence and Lord Kitchener among its members. The fund made two expeditions here, one at the turn of the century and one in 1917, not long after General Edmund Allenby walked into Jerusalem to seal his triumph over the Turks. But there is only one line.
It takes a moment for its meaning to sink in. The fund's Levantine scholars and archaeologists were in a boat when they painted the line to show the level of the Dead Sea. Where we are standing was then four metres underwater. The mystery is what prompted them to mark it at all.
Given that the level had been pretty well stable for the best part of 75,000 years, how were they so prescient as to realise that within half a century or so it would start to fall so catastrophically that a record would be necessary? And that a place, since prehistory the lowest on the planet, would become steadily lower still, so by 2005 the edge of the Dead Sea would be some 500m of cracked and gently sloping sandy, salty flatland east of where, bobbing on what was then its surface, they had carefully painted the line in the cliff?
Perhaps it is not too fanciful to think that they foresaw some of the havoc man would wreak here during the next century. The level of the Dead Sea - now 1,370ft below sea level - is falling fast, by about a metre a year. Since the line was painted, the sea has shrunk by more than a third, or 20km, so the long southern stretch of deep water where King Herod's boat would be moored when he visited Masada is now dry land.
And the reason is not hard to find: the once strongly flowing river Jordan which for so long kept the sea in equilibrium by discharging into it 1.3 billion cubic metres a year of fresh water to replenish what it lost in evaporation is now a pitiful, contaminated trickle, mustering at most 50 million to 100 million cubic metres, a volume itself steadily reducing by the year. And the cause is entirely man-made.
The river has been raped and plundered; first, through the creation of the national water pipeline in the 1950s to meet the needs of an Israeli population which has grown by more than five million since the first pre-state kibbutzim started to divert Jordan water to satisfy their needs for irrigation and drinking water, then through the damming of almost every tributary and wadi that feeds it from the east in an attempt to meet Jordanian and Syrian demands for the region's scarcest resource.
To make the crisis worse, some 60 miles to the north, and just south of the Sea of Galilee, untreated Israeli sewage is pumped into the Jordan, just as further downstream, Jordanian, then Palestinian waste too, has in turn helped to turn the river most revered in Christian, Muslim and Jewish tradition into what Gidon Bromberg, the Israel director of Friends of the Earth Middle East, says is now little more than a sewage canal.
There is no better way of seeing the drama of what is happening to the Dead Sea than to tour it with Mr Bromberg, a passionate Israeli-born environmental lawyer brought up in Australia. As you drive south along Route 90, with its breathtaking views of this inland sea inhabited by no living creature, he points out some of the 1,000 menacing sinkholes which have opened up in little more than a decade as the waters have receded and now threaten to collapse the roads and the still relatively few buildings on its western shore.
As we stop at Mineral Beach, one of the older Dead Sea spas, he says the resort will soon have to close, adding: "The whole earth underfoot is no longer stable. And the road here is at risk; it will probably have to be moved." At the far southern end, is the Dead Sea Works, an unsightly, sprawling factory which makes potash and bromides for fertiliser from the sea's uniquely rich mix of minerals, and with its Canadian-owned Jordanian counterpart, the Arab Potash Company, is responsible for between 25 and 30 per cent of the sea's water loss.
The are many ironies about the Dead Sea's plight. One is that the instability of the shorelines has caused a development freeze which has kept them free of unbridled hotel expansion. Another is that the shrinking of the Dead Sea has made the works an indispensable element of the basin's economy, as Mr Bromberg recognises, although he lobbied fiercely against its attempt to increase production. Apart from the 2,000 jobs it supports, without the huge extraction ponds (which many visitors assume is the Dead Sea itself) into which it pumps the water along a canal, the complex of hotels which once bordered the sea's southern shore would now be surrounded by mud flats and nothing else. "Ideally we'd like to close it, but that's unrealistic because tourism here depends on the ponds," Mr Bromberg says. "But we stopped it expanding." From the field school at the desert oasis of Ein Gedi, where ibex graze a few yards away, he points to a microcosm of the crisis unfolding along the length of the Dead Sea.The Ein Gedi nature reserve is a sanctuary for many of the plants, wildlife, and some 200 species of birds now threatened by the changes in the ecosystem of the Dead Sea basin. But while the Jewish community which lived here in ancient times was "in balance" as he puts it, the David Spring, which tumbles down the hillside now no longer reaches the Dead Sea.
Instead it is "outrageously" - a word Mr Bromberg uses a lot - diverted to the bottling plant below us for the prized mineral water you can buy throughout Israel, or to supply the adjacent kibbutz and irrigate the botanical gardens it tends in the arid desert land. "Ein Gedi isn't the reason for the problems of the Dead Sea," Mr Bromberg says. "But it is a kind of paradigm for what is happening to the sea as a whole."
Nearby is the Ein Gedi Spa, famous for its mud wraps and rich, natural hot-water mineral baths and for its access to the sea. To lie in the waters of the Dead Sea, which famously has a salt concentration 10 times as high as that of the Mediterranean, is an unforgettable experience. With buoyancy so great it is almost impossible, once floating, to lower your legs, you can feel the sting of scratches you never knew you had. You emerge strangely invigorated by the almost oily sensation afforded by the rich mineral composition of the water, and caked with salt. When the spa was constructed in 1986, its clients could walk a few feet to the shore for a bathe. Now it is a kilometre away, so those who do not want to walk take a wagon train hauled by a red tractor.
Covered in black therapeutic mud from head to foot, Omar Taha, 47, an Israeli Arab from a village near Netanya, who has been coming here regularly since the spa opened, points to the repeatedly extended road from the hotel and says: "Of course it bothers me. This is worse every year. This used to be all water. We need to find a solution."
Mr Taha is hardly alone. Of the possible solutions being canvassed, the most dramatic is the long-standing idea of a "peace conduit", or 174km of canal tunnel and pipeline, which would bring sea water from the Gulf of Aqaba to the Dead Sea. The project is colloquially known as "Red-to-Dead " and the World Bank is conducting a $20m (£11m) feasibility study on behalf of all the Dead Sea's "riparian partners", Israel, Jordan and the Palestinian Authority.
Its elegance lies in the way it would use the fact that the Dead Sea is so far below sea level. After initially being pumped or sucked 170km above sea level, the water would then fall 500m into the Dead Sea, with mere gravity generating enough hydro-electric energy to power desalination plants creating up to 850 million cubic metres a year of fresh water, with big potential to ease dire regional water poverty, which leaves easily the worst-off of the partners, the Palestinians, with a mere 70 cubic metres of water per head (compared to 340 for Israel and 1,500 for the UK). At the same time, it is hoped, the Dead Sea will be refilled.
The total project would cost a perhaps a daunting $5bn, but John Stevens, a banker helping to put together a British consortium, believes a basic $500m Red-to-Dead link could be funded by private sector investors buying land then selling it after it is irrigated by desalinated water, for development of a large new trans-border Israeli-Jordanian tourist complex south of the Dead Sea. "At the same time, it would be able to provide a great deal of water to the Jordan Valley which would allow very scarce resources to be freed elsewhere," Mr Stevens says.
As with every large infrastructure project in the world, not everyone is sold on the idea. Mr Bromberg has serious reservations about its ability to solve the Dead Sea crisis. He says the mix of sea water from Aqaba with the Dead Sea could trigger an adverse chemical reaction, creating gypsum, algae and even toxic gases. He is also worries about potential damage to coral reefs in the Gulf of Aqaba from such wholesale extraction, and the potential of salt water to contaminate freshwater supplies if the conduit is damaged in what is an earthquake zone.
With his Palestinian and Jordanian FoE directors, he has been agitating - with limited success - for the World Bank to widen its terms of reference. He says: "We are not trying to rule out Red-to-Dead, only to make sure all the options are considered. We need a truly independent study. Anything less is unacceptable."
Mr Bromberg and his colleagues in Ramallah and Amman want the Dead Sea declared a Unesco World Heritage Site, because the parties would first have to show they can manage the crisis. But his preferred solution is more radical and controversial: abandonment of much of Israel and Jordan's export-oriented, and in his view unsustainable, agriculture to start restoring the waters of the river Jordan, and through it the Dead Sea, again.
Mr Bromberg says 50 per cent of Israel's water resources, including treated sewage, go to agriculture yet the sector's contribution to GDP is just 3 per cent." And farmers buy hugely subsidised water, at 16 US cents per cubic metre when the real price is about $1. In Jordan, he says, 75 per cent of desperately scarce water supplies are going agriculture, which is 6 per cent of GDP.
He sees the problem as political. "In Israel, the kibbutzim have a strong base in the Labour Party and the moshavim an equally strong basis in Likud. In Jordan, some of the very wealthy farmers are the sheikhs and landowners who help to keep the king in power." But in Israel at least, is he not suggesting one of the central pioneering tenets at the heart of its growth is no longer relevant?
"We are challenging the old Zionist concept of making the desert bloom," he says. "Difficult as it is psychologically, we have to move away from desert agriculture, at least for export."
Mr Bromberg believes the future for the Dead Sea area lies in tourism, but carefully controlled and sustainable.
In 150 years the Dead Sea will become so supersaturated with salt that evaporation will halt. But by then, environmentalists say, its size could have reduced by a third, possibly producing the full-scale environmental disaster now threatened. But at last there is hope the crisis is being taken seriously.Reuse content