Eight years ago, a much-discussed study estimated that there were 304 million lakes on Earth—but a careful count reveals that the number is closer to a third of that. The planet holds 117 million lakes, researchers find in what LiveScience calls the "best count yet." And while they may be fewer in number, they take up more of the Earth's surface than scientists had thought: some 3.7% of it, it turns out. Experts used computers to count the bodies of water using high-resolution satellite images. "This is something one would have assumed had been done long ago, and was in a textbook somewhere," says a researcher.
One reason it wasn't: Most lakes are far from human residences, and millions are so small they haven't appeared on maps, LiveScience reports. Indeed, 90 million of the lakes counted were between 0.5 to 2.5 acres, or less than two football fields. The new figure measures the lakes around today, a number that can easily change; indeed, the Aral Sea, once the fourth-biggest lake on Earth, is now almost dry, the Independent reports. So what's the point of all this counting? "If we are to be able to make realistic estimates of the collected effects of the different processes in lakes, for example their contribution to global warming, we first need a good map," a researcher says in a press release. (Of course, we're not the only planet with lakes.)