Until now, no one knew for sure how many lakes exist on Earth.
Blame geography — most of the world’s lakes are in places where humans don’t live, said David Seekell, an environmental scientist at Umea University in Sweden. “This is something one would have assumed had been done long ago, and was in a textbook somewhere,” Seekell said.
Lake size was a liability, too. Millions of lakes are too small for mapmakers to bother charting.
Instead of counting lake by lake, earlier estimates were statistical guesses, based on the number of lakes in a parcel of land or on average lake size. One widely cited study from 2006 estimated the lake total at 304 million.
A new study published Sept. 16 in the journa Geophysical Research Letters sidesteps these problems. With high-resolution satellite data and supercomputers to check every cloudless pixel, researchers now have the best count yet of lakes on Earth. The result? There are 117 million lakes in the world.
Yet the bodies of water cover more land (3.7 percent of Earth’s surface) than previous studies had predicted. This is because quite a few medium- to large-size lakes were missing from the databases used for previous studies.
About 90 million of the lakes fall in the smallest size category, measuring 0.5 to 2.5 acres (0.2 to 1 hectare), the study reports. That’s equal to a country house lot, a large farm pond or 1.9 American football fields.
"Most lakes are in the far North, and there’s actually quite a few of them," said Seekell, a co-author of the new study. "Even if they’re small and no one sees them, they are potentially important for global-scale environmental issues like the carbon budget," he told Live Science.