Hydraulic fracturing (fracking) fluids spilled in 2007 from natural gas wells are believed to be the cause of “widespread death or distress” of an aquatic species in a small Appalachian creek in Kentucky, based on a joint study by the U.S. Geological Survey (USGS) and the U.S. Fish and Wildlife Service (FWS).

The Acorn Fork, designated by Kentucky as an “Outstanding State Resource Water,” is habitat for the federally threatened Blackside dace, a small colorful minnow that has been listed as “threatened” by the FWS since 1987. The fish are found only in the Cumberland River Basin of Kentucky and Tennessee, and the Powell River Basin of Virginia.

“Our study is a precautionary tale of how entire populations could be put at risk even with small-scale fluid spills,” said USGS scientist and lead author Diana Papoulias. “This is especially the case if the species is threatened or is only found in limited areas, like the Blackside dace is in the Cumberland.”

The Blackside dace, which primarily is threatened by loss of habitat, typically lives in small, semi-isolated groups, and “harmful events” risk completely eliminating a local population.

After a chemical fluid spill during gas drilling operations in 2007, state and federal scientists observed a “significant die-off of aquatic life in Acorn Fork including the Blackside dace, as well as several more common species like the Creek chub and Green sunfish.” Officials were alerted to the incident by an area resident who apparently witnessed the die-off.

To determine the cause of the fish die-off, the researchers collected water and fish samples following the chemical 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,” the report noted.

The report, “Histopathological Analysis of Fish from Acorn Fork Creek, Kentucky Exposed to Hydraulic Fracturing Fluid Releases,” was published in Southeastern Naturalist, a scientific journal.

The FWS and the Commonwealth of Kentucky now are working toward restoring the natural resources injured by the release.

“This is an example of how the smallest creatures can act as a canary in a coal mine,” said the study’s co-author Tony Velasco, a FWS ecologist based in Kentucky. Velasco initiated a multi-agency response when the spill 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 found by scientists “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.”

According to the study, once the chemical fluids entered the creek, the water’s pH dropped to 5.6 from 7.5, while stream conductivity increased to 35,000 from 200 microsiemens/centimeter. “A low pH number indicates that the creek had become more acidic, and the stream conductivity indicated that there were higher levels of dissolved elements including iron and aluminum.”