A joint study by the U.S. Geological Survey and the U.S. Fish and Wildlife Service is pointing to natural gas fracking as the cause of widespread death of fish in an Eastern Kentucky stream.The report found that hydraulic fracturing fluids—which are used to help extract the gas from the ground—spilled from a natural gas well site near Acorn Fork in 2007. After that, scientists saw a sharp decline in aquatic life in the stream. One of the species affected—the Blackside dace—is federally threatened.From the press release: The samples analyses and results clearly showed that the hydraulic fracturing fluids degraded water quality in Acorn Fork, to the point that the fish developed gill lesions, and suffered liver and spleen damage as well. “This is an example of how the smallest creatures can act as a canary in a coal mine,” said Tony Velasco, Ecologist for the Fish and Wildlife office in Kentucky, who coauthored the study, and initiated a multi-agency response when it occurred in 2007. “These species use the same water as we do, so it is just as important to keep our waters clean for people and for wildlife.” The gill lesions were consistent with exposure to acidic water and toxic concentrations of heavy metals. These results matched water quality samples from Acorn Fork that were taken after the spill.