This natural-color satellite image shows small blue and green lakes in northern Siberia, near the Gulf of Ob. 
 
 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. [5 Surprising Facts About Lakes ] 
 
 A new study published Sept. 16 in the journal 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 older databases, said Cory McDonald, a research scientist with the Wisconsin Department of Natural Resources, who was not involved in the study. 
 
 "I was surprised that the total surface area they measured was much greater than previous estimates," said Cory McDonald, a research scientist with the Wisconsin Department of Natural Resources, who was not involved in the study. "We knew there problems with the extrapolation methods used to fill the data gap for the small lakes, but previous estimates assumed we had a pretty good handle on the medium- to larged-sized ones," he told Live Science in an email interview. "This study largely puts to rest the long-debated questions of 'How many lakes there are in the world and how much surface area do they cover?'" 
 
 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. 
 
 Climate scientists believe lakes influence greenhouse gas levels in the atmosphere. Lakes pump out carbon dioxide and methane — both greenhouse gases — but they can also lock away carbon for centuries by trapping it in their cool bottom muds. Without an accurate count, the role of lakes is difficult to assess, Seekell said. 
 
 According to the new results, the world's lakes cover about 2 million square miles (5 million square kilometers), which is 3.7 percent of the land uncapped by glaciers. 
 
 Most lakes are in the Northern Hemisphere between 45 degrees north latitude and 75 degrees north latitude. (Think about Canada, Russia, Alaska, Northern Europe and the Great Lakes.) This results from the tectonic scattering of continental landmasses and the past positions of glaciers, the researchers said. There is less land in the southern high latitudes, and the North's sizable plains were scraped by ice age glaciers, leaving behind millions of pothole lakes. 
 
 The majority (85 percent) of Earth's millions of lakes are at low altitudes, found at elevations less than 1,600 feet (500 meters) above sea level. 
 
 The study excluded the Caspian Sea, the world's largest lake, which covers an area of about 143,000 square miles (371,000 square km). Antarctica and Greenland were also left out of the study. (Antarctica has about 400 lakes buried by ice.) 
 
 The researchers plan to freely release the lake database, Seekell said. They also intend to update the count with higher-resolution data from the Landsat 8 satellite. 
 
 "Lakes are not static on the landscape, and in some parts of the world, they are disappearing quite quickly," Seekell said. 
 
 In certain regions of Russia and Alaska, higher temperatures are causing what was once permanently"frozen ground, called permafrost, to thaw, causing small lakes to dry up. Melting permafrost under a lake is like a cracked tub liner — the lakes drain out from their bottoms. Drought and overuse are also shrinking lakes. In northern China, for instance, more than 100 lakes disappeared during the 2000s from these causes. 
 
 Email Becky Oskin or follow her @beckyoskin. Follow us @livescience, Facebook & Google+. Original article on Live Science. ||||| Antarctica's Dry Valleys are the most arid places on Earth, but underneath their icy soils lies a vast and ancient network of salty, liquid water filled with life, a new study finds. 
 
 The Dry Valleys are almost entirely ice-free, except for a few isolated glaciers. The only surface water is a handful of small lakes. Inside the canyons, the climate is extremely dry, cold and windy; researchers have stumbled upon mummified seals in these gorges that are thousands of years old. 
 
 Yet there is life in this extreme landscape. For instance, bacteria living under Taylor Glacier stain its snout a deep blood red. The rust-colored brine, called Blood Falls, pours into Lake Bonney in the southernmost of the three largest Dry Valleys. The dramatic colors offer shocking relief to senses overwhelmed by the glaring white ice and dull brown rocks. [The 10 Driest Places on Earth] 
 
 Now, for the first time, scientists have traced the water underneath Taylor Glacier to learn more about the mysterious Blood Falls. In the process, the researchers discovered that briny water underlies much of Taylor Valley. The subsurface network connects the valley's scattered lakes, revealing that they're not as isolated as scientists once thought. The findings were published today (April 28) in the journal Nature Communications. 
 
 "We've learned so much about the dry valleys in Antarctica just by looking at this curiosity," said lead study author Jill Mikucki, a microbiologist at the University of Tennessee, Knoxville. "Blood Falls is not just an anomaly, it's a portal to this subglacial world." 
 
 Mikucki led an international research team that tested a newly developed airborne electromagnetic sensor in Taylor Valley. The flying contraption is a large, six-sided transmitter suspended beneath a helicopter. The instrument creates a magnetic field that picks up conductivity differences in the ground to a depth of about 1,000 feet (300 meters). 
 
 "Salty water shone like a beacon," Mikucki said. 
 
 A helicopter flies a transmitter across Lake Frxyell, Antarctica. Credit: L. Jansan 
 
 The researchers found liquid water underneath the icy soil in Taylor Valley, stretching from the coast to at least 7.5 miles (12 kilometers) inland. The water is twice as salty as seawater, the scientists reported. There is also briny water underneath Taylor Glacier as far back as the instrument could detect, about 3 miles (5 km) up the glacier, the researchers said. Eventually, the ice was too thick for the magnetic field to penetrate. 
 
 "This study shows Blood Falls isn't just a weird little seep," Mikucki told Live Science. "It may be representative of a much larger hydrologic network." 
 
 Water underneath Taylor Valley could have turned extremely salty in two ways: The brines could be due to freezing and evaporation of larger lakes that once filled the valley. Or, ocean water may have once flooded the canyons, leaving remnants behind as it retreated. The new findings will help researchers pin down the valley's aquatic history. 
 
 "I find it a very interesting and exciting study because the hydrology of the Dry Valleys has a complicated history and there's been very little data abut what's happening in the subsurface," said Dawn Sumner, a geobiologist at the University of California, Davis, who was not involved in the study. 
 
 Scientists are also intrigued by the new results because the Dry Valleys are considered one of the closest analogs to Mars that are located on Earth. Similar briny groundwater could have formed on Mars when the planet transitioned from having liquid water to a dry environment, Sumner said. 
 
 Finally, the findings may change views of Antarctica's coastal margins, Mikucki said. Now that scientists know Taylor Valley's groundwater seeps into the ocean, further research may reveal that coastal regions are important nutrient sources for Antarctica's iron-depleted seas, she said. 
 
 Follow Becky Oskin @beckyoskin. Follow Live Science @livescience, Facebook & Google+. Originally published on Live Science.
– 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.)