When it’s too late, we’ll realize the signs were obvious. We’ll look back at the staggering 83% decline in freshwater species populations – more than twice the rate of terrestrial and marine – and wonder why we didn’t take action to safeguard the rivers and lakes in which these species thrive. We’ll remember the Mekong River’s role in providing clean water, fish and rice to feed us, livelihoods and a healthy delta in Vietnam when those are diminished.

We are at a critical point for deciding the fate of the Mekong, and other rivers worldwide. If we continue to degrade them through mega dams, industrial-scale sand extraction and unsustainable diversion for agriculture, we will lose more than we realize.

For the first time, scientists have comprehensively mapped the state of our world’s free-flowing rivers. They found that only about one-third (37%) of the world’s longest rivers remain free-flowing – unobstructed by human activity. Their study also found that dams are the leading contributors to connectivity loss in river systems. Dams modify the natural flow of rivers and fragment their habitats. This in turn affects movements of species and flows of water, nutrients and sediments, which ultimately degrades the natural systems and the many benefits that they provide to humans.

Free-flowing rivers are among the most important freshwater habitats in terms of biodiversity and certain ecosystem services. These include providing abundant fisheries that feed millions, nutrients to downstream floodplains and agriculture, sediments that help stop deltas from sinking, refuges for biodiversity in a rapidly changing world, and healthy wetlands that act as a buffer against extreme weather events.

Rivers, more generally, are among the most diverse and productive ecosystems on the planet; they underpin entire landscapes and contribute to economic growth, food security and human well-being. Globally, 2 billion people rely on rivers for drinking water, 25% of the world’s food production depends on irrigation from rivers and at least 12 million tons of freshwater fish are caught each year, providing food and livelihoods for hundreds of millions of people.

We are now in the middle of a planned hydropower boom: More than 3,700 hydropower dams are currently proposed or under construction. If these plans are realized, we could see a loss of hundreds of thousands of kilometers of free-flowing rivers and the diverse benefits they provide

We are now in the middle of a planned hydropower boom: More than 3,700 hydropower dams are currently proposed or under construction. If these plans are realized, we could see a loss of hundreds of thousands of kilometers of free-flowing rivers and the diverse benefits they provide.

In the coming years, a combination of infrastructure and climate change will only further increase the pressure on rivers. Rising temperatures will impact flow patterns, water quality and biodiversity, while dam construction continues to segment rivers, trap sediment, and impede movements of freshwater species.

In the Greater Mekong Region, Cambodia’s proposed Sambor Dam would be an 18km-wide behemoth that could signal the end of the enormously productive Vietnam Delta, massive declines in fisheries and the extinction of the river’s critically endangered Irrawaddy dolphins. When combined with the other proposed Cambodia dam – Stung Treng – the effects will be devastating and long-lasting.

Fortunately, there is hope.

There is potential for us to learn from past mistakes. We can develop infrastructure in a way that preserves our rivers yet meets our needs, which in turn safeguards critical resources for humans and nature for decades to come.

Currently, dams are often sited and built at an individual project level. We need early basin- or system-scale planning that, first, examines whether alternative green infrastructure or renewable energy options are available and, second, sites dams or other infrastructure in a way that accounts for not only energy- or water-provision needs, but also ecosystem health, local livelihoods, economic feasibility, and other important measures.

For example, in the case of hydropower dams, while hydro energy emits fewer emissions than coal, dams can have large environmental and social impacts. Additionally, recent studies have shown that dams usually run over budget and take much longer to construct than originally scheduled, with average cost overruns of 96% and delays of 44% longer than predicted. As the costs of wind- and solar-energy options decline, countries may be able to meet a large proportion of their energy needs without compromising remaining free-flowing rivers, and the communities, cities and biodiversity that rely on them.

An expansion of national legal protections can also aid in the protection and preservation of the world’s free-flowing rivers. Mexico, with its recent designation of water reserves, provides an example of a legal protection that bars river disruptions due to poor planning and carefully allots water reserves to avoid over-consumption. This framework calls for comprehensive planning that helps to keep certain rivers free-flowing, while still meeting important domestic, industrial and energy needs. In other words, through sustainable infrastructure planning and design we can preserve natural river flows while meeting human needs.

Free-flowing-rivers research is critical for us to build a future in which rivers, and the value they provide, remain on our planet – and in our country. The Mekong is at a critical moment in its history. Will we dam it, sand-mine it and degrade it out of existence, or will we maintain its natural flow, manage it sustainably and invest in alternative energy sources like solar that don’t result in the destruction of the Mother River of Asia?