According to the Associated Press, the decision stemmed from a lawsuit the Sierra Club brought against the EPA last year claiming the government had evidence that the Nogales International Wastewater Treatment Plant, in Nogales, Ariz., was polluting the Nogales Wash and the Santa Cruz River.

Environmentalists sued the plant operators: the International Boundary and Water Commission and the city of Nogales. But they also sued the EPA. The Sierra Club reached an out-of-court settlement with the city and water commission to clean up the plant, but appealed a federal judge's decision barring the group from demanding that the EPA take action against the plant.

The 9th U.S. Circuit Court of Appeals noted the EPA, like criminal prosecutors, are immune from suits for actions they do not take. The appeals panel said the government, not the judiciary, should decide what environmental action should be done, just as prosecutors decide whether to charge a suspected criminal.

Joy Herr-Cardillo, a Sierra Club attorney, said the group is considering asking the Supreme Court to review the decision, the AP reported.