From the Tigris to the Indus and the Yangtze to the Nile, rivers were essential to the emergence of human civilisation. Millennia later, hundreds of millions of people still depend on rivers to quench their thirst, grow food and make a living. And yet we are rapidly destroying the planet’s river systems, with serious implications for our economies, societies and even our survival.

China is a case in point. Its dam-building frenzy and overexploitation of rivers are wreaking environmental havoc on Asia, destroying forests, depleting biodiversity and straining water resources. China’s first water census, released in 2013, showed that the number of rivers—not including small streams—had plummeted by more than half over the previous six decades, with over 27,000 lost.

The situation has only deteriorated since then. The Mekong River is running at a historically low level, owing largely to a series of Chinese-built mega-dams near the border of the Tibetan Plateau, just before the river crosses into Southeast Asia. In fact, the Tibetan Plateau is the starting point of most of Asia’s major rivers, and China has taken advantage of that, not least to gain leverage over downstream countries.

China may be the world’s largest dam builder, but it isn’t the only one; other countries, from Asia to Latin America, have also been tapping long rivers for electricity generation. The diversion of water for irrigation is also a major source of strain on rivers. In fact, crop and livestock production absorbs almost three-quarters of the world’s freshwater resources, while creating runoff that, together with industrial waste and sewage discharge, pollutes those very resources.

In total, almost two-thirds of the world’s long rivers have been modified, and some of the world’s longest—including the Nile and the Rio Grande—now qualify as endangered. Of the 21 rivers longer than 1,000 kilometres that still flow freely from their mountain sources to the sea, most are in remote regions of the Arctic and in the Amazon and Congo basins, where hydropower development is not yet economically viable.

These trends strain water resources, destroy ecosystems and threaten human health. For example, heavy upstream diversions have turned the deltas of the Colorado River and the Indus River into saline marshes. Lower river levels impede the annual flooding cycle, which in tropical regions helps to re-fertilise farmland naturally with nutrient-rich sediment. In periods of below-average rainfall, a number of rivers increasingly run dry before reaching the ocean, and even when they do make it, they are depositing less of the nutrients and minerals that are vital to marine life.

Globally, aquatic ecosystems have lost half of their biodiversity since the mid-1970s, and about half of all wetlands have been destroyed over the last century. A recent United Nations study warned that up to a million animal and plant species are threatened with extinction, many within decades.

Humans are hardly exempt from the health consequences of river destruction. In Central Asia, the Aral Sea has all but dried up in less than 40 years, owing to the Soviet Union’s introduction of cotton cultivation, for which water was siphoned from the sea’s principal sources, the Amu Darya and Syr Darya rivers. Today, particles blown from its exposed seabed—thick with salts and agricultural chemical residue—not only kill crops, but are making local people ill with everything from kidney disease to cancer.

Free-flowing rivers play a critical role in moderating the effects of climate change by transporting decaying organic material and eroded rock to the ocean. This process draws about 200 million tons of carbon out of the air each year.

In short, the case for protecting our rivers could not be stronger. Yet, while world leaders are often willing to pay lip service to the imperative of strengthening river protections, their rhetoric is rarely translated into action. On the contrary, in some countries, regulations are being rolled back.

In the US, almost half of rivers and streams are considered to be in poor biological condition. Yet last October, President Donald Trump’s administration repealed the ‘Waters of the United States’ rule, which had been introduced by his predecessor, Barack Obama, to limit pollution of streams, wetlands and other bodies of water. Last month, the Trump administration replaced it with a far weaker version, called the ‘Navigable Waters Protection Rule’.

In Brazil, President Jair Bolsonaro has relaxed environmental rules in the name of economic growth. Among the casualties is the Amazon River, the world’s largest river in terms of discharge, which carries more water than the next 10 largest rivers combined. Already, the Amazon basin in Brazil has lost forest cover over an area bigger than the entire Democratic Republic of the Congo—the world’s 11th-largest country.

The absence of water-sharing or cooperative-management arrangements in the vast majority of transnational river basins facilitates such destruction. Many countries pursue projects without regard for their cross-border or environmental effects.

One way to protect relatively undamaged river systems—such as the Amur, the Congo and the Salween—would be to broaden implementation of the 1972 World Heritage Convention and add these rivers to the World Heritage List, alongside UNESCO World Heritage Sites. This would be in line with recent efforts in some countries—Australia, Bangladesh, Colombia, India and New Zealand—to grant legal rights to rivers and watersheds. For such initiatives to work, however, effective enforcement is essential.

As for the rivers that are already damaged, action must be taken to restore them. This includes artificially recharging rivers and aquifers with reclaimed wastewater, cleaning up pollution, reconnecting rivers with their floodplains, removing excessive or unproductive dams, and implementing protections for freshwater species.

The world’s rivers are under unprecedented pressure from contamination, damming and diversion. International cooperation can save them, but first we must recognise the consequences of doing nothing.