The Freshwater Ecosystems Explorer was developed as part of a UN effort to track progress on the environmental basis of Sustainable Development Goal 6, which calls for everyone on Earth to have access to clean water and sanitation by 2030. Headway towards the goal is halting: in 2022, 2.2 billion people still lacked access to safely managed drinking water.  

Part of the reason for the shortage is what experts call a worrying state of freshwater ecosystems, which along with lakes, rivers and wetlands include aquifers, mangrove forests and glaciers. A UNEP-backed report from 2024 found that nearly half the countries on Earth had at least one significant freshwater ecosystem in decline. The report blamed the falloff on a range of factors including climate change, which is making many places drier, overusing water, constructing dams, and converting freshwater ecosystems, like wetlands, into farms or urban areas.  

Many of those challenges have been laid bare by the Freshwater Ecosystems Explorer, which charts any body of water on the Earth’s surface larger than 30 metres by 30 metres. It offers what experts call an unprecedented level of detail, tracking not only pollution but also the size of freshwater bodies, some over the course of decades.  

It shows, for example, how years of drought led to the near-calamitous shrinking of South Africa’s Lake Kariba, which supplies the city of Cape Town with drinking water. It also reveals how a surge in rainfall in the United Kingdom and Northern Ireland, which has been linked to climate change, caused rivers to burst their banks, leading to widespread flooding. 

And it gives a bird’s eye view of Lake Titicaca, which sits in a basin home to 3 million people and is fed by glacial melt. The largest lake in South America is careening towards collapse, experts say, in part because of the dumping of raw sewage. Satellite data shows where the water is becoming increasingly cloudy, or turbid, and where there has been a surge in nutrient levels, two telltale signs of pollution. This runoff affects ecosystems, human health and biodiversity. 

Not all news was bad, though. The explorer has charted the rebound of several bodies of water, including Iran’s Lake Urmia where an effort to unblock its feeder rivers have caused water levels to rise in a lake once thought near dead. 

That was part of a larger trend that has seen countries revive many freshwater bodies, including some of the world’s most-polluted urban rivers.  

Restoring freshwater ecosystems and other inland water bodies is a key aim of the Kunming-Montreal Global Biodiversity Framework, a landmark 2022 agreement to halt and reverse the decline of the natural world.