T HE RIVER VIEW HOTEL on the banks of the Yamuna river at Okhla, on the outskirts of Delhi, lives up to its name. But the view is not uplifting. Rubbish is strewn along the water’s edge. As elsewhere in India, industrial pollution, untreated sewage and the still widespread practice of open defecation make this stretch of the Yamuna a toxic soup teeming with bacterial infection. According to India’s Central Pollution Control Board ( CPCB ), in 2016 the water contained at times 1.6bn faecal coliform bacteria per 100ml—more than 3m times the CPCB’S “desirable” bathing limit of 500 per 100ml.

About 600km (373 miles) downstream from Okhla the sacred Yamuna joins an even holier river, the Ganges, or Ganga, at Prayagraj (formerly Allahabad), site from January to March this year of the six-yearly kumbh, a Hindu festival that is expecting 150m devotees—perhaps the largest human gathering ever held anywhere. They have waited for days for the chance to cleanse their souls, if not their bodies, by taking a short dip (limited to 41 seconds, in an effort to avert stampedes) in the blessed waters. The river there is considerably less toxic. In December the CPCB ordered state governments to stop “grossly polluting units”—distilleries, paper mills and textile factories—discharging effluent into the river. The Tehri dam upstream released more water to ensure it flowed just fast enough to wash away sins but not sinners.

Even farther downstream, the Ganges reaches Varanasi, Hinduism’s holiest city and the parliamentary constituency of India’s Hindu-nationalist prime minister, Narendra Modi. Year-round, devotees visit to bathe or drink the waters, or to cremate their dead on the ghats, the series of broad stone staircases that line the southern bank. One of Mr Modi’s first and most fervent pledges in office was to clean up the Ganges, to ensure its “purity and uninterrupted flow”. He renamed the Ministry of Water Resources by adding to its title “River Development and Ganga Rejuvenation”.

But the water remains polluted and dangerous to health, and the Ganges’ flow is weakening, in part because of the hydroelectric dams on its upper reaches. A study in 2018 found its flow in some stretches may have fallen by 50% since the 1970s. Climate change has actually encouraged the damming of the river. By one reckoning about 70% of the Ganges’ flow is contributed by meltwater from the Himalayan glaciers from where it springs. Engineers had assumed that, as temperatures rise, more ice would melt, increasing the river’s flow and hence its hydroelectric potential. In fact, it has declined in the past few years, because the aquifers supplying Himalayan rivers have been shrinking as winter precipitation drops. In the long run, however, the fate of the glaciers might doom the great rivers. A study published in February by the International Centre for Integrated Mountain Development, a think-tank in Nepal, warned that even on relatively benign forecasts of global warming, more than a third of Himalayan glaciers will have melted by 2100, with river flows declining from the 2060s.

The state of the holy river is worth dwelling on. Some 400m people—5% of humanity—live on its plains. But it may also be the most powerful symbol anywhere of the sheer difficulty of managing freshwater supplies. As Victor Mallet, a British journalist, asks in his book on the Ganges, “River of Life, River of Death”, “Why do Indians and their governments tolerate for even a week the over-exploitation of their holy river—sometimes to the point of total dehydration—by irrigation dams and its poisoning by human waste and industrial toxins?” After five years of government under Mr Modi, that question remains unanswered.

The clean-up effort has two main elements. The first involves a nationwide campaign, known as swachh bharat (clean India) to end open defecation, in which India in 2014 led the world, with 600m open defecators out of a global total of 1bn. Thanks to subsidies for the construction of 92m toilets (mostly simple twin-pit arrangements that turn faecal sludge into harmless compost), the government says the “ ODF ” (open-defecation free) rate has risen from 39% in 2014 to 99% now. Many scoff at such hyperbole, but, at the very least, in many places to venture at dawn through the Indian countryside is no longer to intrude on a mass latrine.

The second aim, building treatment plants, has been beset by disagreements over the design of the scheme. Private companies are to bid for treatment contracts, with payment partly based on sensors tracking the water they produce. They are handicapped by the lack of sewers in much of India, so in many cases they will have to block discharges with weirs to divert them for treatment.

If such a sacred source is so hard to rescue, what hope for other ravaged rivers and lakes, in India and elsewhere? For his book “When the Rivers Run Dry”, published in 2006 and recently updated, Fred Pearce, a British writer, visited dozens of countries around the world and writes of river after river under seemingly life-threatening stress. Three of the rivers have, since Mr Pearce’s first visit, become test-cases for different approaches to solving surface-water problems: large-scale infrastructure to bring water from elsewhere; flow-management through digital monitoring; and the use of economic levers.

In Israel, the state of its famous sources of surface water—the River Jordan and the Sea of Galilee (in fact, a freshwater lake)—is also a national preoccupation. After five years of its worst drought in nearly a century, the level of the Sea had sunk late last year to alarming levels. Heavy rains in December and January ended the crisis, but Israel’s supply of natural freshwater remains precarious, according to Uri Schor of Israel’s water authority.

For much of Israel’s history, Galilee supplied most of its drinking water. Under the British mandate over Palestine, economists used to worry that immigration into the territory would overwhelm its available water resources. In 1939, 834,000 people lived there. The upper limit was seen as 2m. Israel now has 8.7m inhabitants, with another 5m people living in the occupied territories. They no longer rely on the Sea of Galilee for water. More than half the water Israel uses is man-made, from desalinated seawater (see article) and treated effluent. So during the drought the 400m cubic metres that used to be pumped annually from the Sea was cut, to less than 70m in 2018. Now Israel plans to replenish it with desalinated water so it will form a strategic water reserve.

For now, though, the Sea of Galilee is probably more important to tourists and pilgrims. They can also survey the River Jordan, which runs south into the Dead Sea, the fast-evaporating saltwater lake at Earth’s lowest point on dry land (430 metres below sea-level). The Jordan has long disappointed visitors expecting to see the “deep and wide” waterway from which Michael rowed his boat ashore. In places it can be crossed with a standing jump.

The Yellow River in China, the world’s seventh-longest at 5,500km, now counts as a success story. It gets its colour, and name, from the loess-soil sediment it carries downstream. Its fertile basin was the cradle of Chinese civilisation and, in an epithet often given the river, its “sorrow”. A build-up of sediment changed the river’s course 26 times before 1949. But the sediment also raises the river above the surrounding plains, so that it has to be contained by dykes. Often it has flooded, catastrophically. The risk of floods remains, but a massive dam at Xiaolangdi in Henan province enables engineers to release water to flush the sediment downstream, reducing the danger.

By 2015 this system had also more than doubled the channel’s capacity. But it was still only two-thirds what it had been 50 years before. Indeed, in recent years the river’s drying out has been as big a concern as its flooding. By 1997 it was so overused that it only reached the sea 139 days in the year. At that stage 40% of its waters were too polluted even for irrigation. The quality has much improved but by 2017 water in one-tenth of samples taken from the Yellow River was still deemed unfit for farming. Since then digital centralised controls over the release of water from dams have been introduced. Billed as the world’s most advanced water-rationing system, this has kept the flow to the sea uninterrupted. Environmentalists, however, complain that the dams have harmed the river’s ecosystem, and that pressure has shifted from the river itself to its increasingly polluted tributaries and underground aquifers, which are shrinking alarmingly.

In Australia, the Murray river, with its main tributary, the Darling (known as the Murray-Darling basin), drains one-seventh of the country, a region the size of France and Spain combined. It irrigates farms, and supplies cities in the east. When Mr Pearce visited the region in 2006 drought had already lasted more than a decade, yet he was shocked to find local farmers insouciant about squandering water, using wasteful flood irrigation, for example, when the water was available. Since the 1970s enormous farms growing thirsty crops such as cotton and nuts had spread across the basin.

That disastrous drought prompted government action to restore the river—if not to its heyday, when paddle-steamers plied it, then at least to levels where it could sustain the farms and people that rely on it. Australia already had an elaborate system for trading water rights, allowing farmers to buy or sell entitlements according to their need in any given season. An index compiled by Aither, a consultancy, tracks a weighted price for these entitlements in the Murray-Darling basin, and showed a 96.1% rise in the ten years from July 2008. The government’s plan aimed to reduce water consumption by at least 2.75 cubic km a year, or about a fifth, either by purchasing water licences from farmers who were willing to offload them, or by financing projects that would save water (eg, through more efficient irrigation).

Water usage was cut by two-thirds of this target, recovering 2.1 cubic km of the surface water. In 2016 the state of South Australia saw its highest flows since 1993. Yet by last year the river was again low, with hundreds of kilometres running dry, entitlement prices rising fast and fish dying in huge numbers. Scientists concluded the basin as a whole was yet to show real improvement.