Earlier this year, researchers published a paper in Molecular Ecology saying that the biodiversity of an area could be determined by closely studying the DNA derived from skin cells, scales, or waste found in soil samples. Now, says Scientific American's Sophie Bushwick, another team of researchers has published a paper in Molecular Ecology with a similar bent. The study found that the biodiversity of a freshwater habitat can be determined by closely studying the DNA in a sample of water from that habitat. "As animals swim through a lake, they leave behind traces of DNA. The more individuals of a particular species, the more DNA of that species will be shed. And be available to be measured," Bushwick says. When the researchers tested their method in about 100 European lakes and streams, she adds, they were able to correctly identify the "denizens" of these habitats as well as the sizes of their populations.