The US Environmental Protection Agency says hydraulic fracturing to drill for oil and natural gas poses a risk to drinking water in some circumstances.
But it says a lack of information prevents a definitive statement on how severe the risk is.
The new report removes a finding from a draft issued last year indicating that fracking has not caused widespread harm to drinking water in the United States.
Industry groups hailed the finding as proof that fracking is safe, while environmental groups focused on cases of fracking-caused pollution cited in the report.
The final report draws no conclusions on fracking’s overall effect on drinking water.
The Associated Press