At first, the satellite image of Lake Titicaca, which sits high in the Andes Mountains on the border between Bolivia and Peru, looks normal. But zoom in, and you’ll see a riot of reds, yellows and greens along its coastlines.
The colours graphically represent pollution – much of it raw sewage and farm runoff – flowing into the lake from surrounding communities.
The satellite image is part of the Freshwater Ecosystems Explorer, a groundbreaking data platform developed by the United Nations Environment Programme (UNEP) and partners that shows the health of millions of lakes, rivers and wetlands around the world. The online site is designed to shine a spotlight on the state of the planet’s freshwater ecosystems and the reserves they hold, which experts say are under mounting pressure from climate change, pollution and a host of other threats.
“Fresh water is fundamental to life on this planet and the website is enabling access to what is vital information,” said Sinikinesh Jimma, head of UNEP’s Marine and Freshwater Branch. “The more people know about the state of their local freshwater bodies, the more they can do to protect and restore them.”
Jimma made the comments just ahead of World Water Day, which falls on March 22 and is designed to raise awareness about the importance of better managing freshwater resources. This year, the day will focus on the preservation of glaciers, which are in retreat in many places around the world.
Eye in the sky
Want to check out the health of a lake, river or aquifer near you? You can begin with a quick introduction to the Freshwater Ecosystems Explorer, which draws on data from a range of sources, including satellites. Once you’re ready, you can dive into the explorer proper, where you’ll find detailed information on the extent and state of freshwater bodies around the world.
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.
"The explorer highlights how robust data can help countries manage their freshwater resources in a more holistic, more integrated way,” said Jimma. “That is crucial to safeguarding this most precious of resources for generations to come.”
The Freshwater Ecosystems Explorer was developed by UNEP, UNEP-DHI, the European Commission Joint Research Centre and Google.
The planet is experiencing a dangerous decline in nature. One million species are threatened with extinction, soil health is declining and water sources are drying up. The Kunming-Montreal Global Biodiversity Framework sets out global targets to halt and reverse nature loss by 2030. It was adopted by world leaders in December 2022. To address the drivers of the nature crisis, UNEP is working with partners to take action in landscapes and seascapes, transform our food systems, and close the finance gap for nature.
