From the Associated Press:

A federal report is blaming a spill of hydraulic fracturing fluids for harming a fish population in a small stream in southeastern Kentucky.

The study by the U.S. Geological Survey and the Fish and Wildlife Service says the liquids are believed to be the cause of a die-off of Blackside dace that lived in the Acorn Fork, a small creek in Knox County. The small minnow-like fish is considered at risk by federal officials due of a loss of habitat.

The spill occurred in 2007, and officials collected samples shortly after.

The federal scientists said after the fluids were released into the stream, the pH of the water dropped from 7.5 to 5.6, meaning it became more acidic. Fish in the stream developed gill lesions, and suffered liver and spleen damage, the study said. The lesions were consistent with exposure to acidic water and toxic concentrations of heavy metals, officials said.

"Our study is a precautionary tale of how entire populations could be put at risk even with small-scale fluid spills," USGS scientist Diana Papoulias, said in a statement on Wednesday.

Hydraulic fracturing, commonly known as fracking, is a method used to extract underground natural gas using high-pressure injections of fluid.

After the spill, a local resident notified authorities of the fish kill in the small stream. Along with the Blackside dace, other aquatic life including the Creek chub and Green sunfish were also harmed, the statement said.

The report was published in the scientific journal Southeastern Naturalist, in a special edition devoted to the Blackside dace.

Federal and state officials are restoring the natural resources that were injured by the release.