There are more than 100 million lakes dotting the planet, according to one prominent study. 

But many aren’t what they used to be. From Bolivia to South Africa and beyond, climate change, pollution and over-abstraction are drastically changing these bodies of water. Many have dwindled to nothing. Others are bursting their banks. Some have even turned green. “Today, some of the world’s best-known and most important lakes are a shadow of what they were just a few decades ago,” says Dianna Kopansky, the head of the Freshwater Ecosystems and Wetlands Unit of the United Nations Environment Programme (UNEP). “We need to reverse this decline. If we don’t, it could be calamitous for the hundreds of millions of people who rely on lakes for their survival.” 

Ahead of the first World Lake Day, which is 27 August, here’s a closer look at the biggest threats to the world’s lakes – and what can be done about them.