Ruth Patrick and her team were trying to judge the condition of Pennsylvania’s Conestoga River Basin in 1948, when they went into the streams, collected organisms and examined the mix of life living there, from microscopic algae and protozoa to aquatic insects and fish. Patrick, a biologist and limnologist at Philadelphia’s Academy of Natural Sciences, had been studying diatoms, which are microscopic algae whose species and abundance could vary with environmental conditions. The archive of her papers at Drexel University says that her work led her to recognize that the variety and composition of organisms in a stream could indicate how polluted it was.
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