In a 6-3 decision, the U.S. Supreme Court ruled in Entergy Corporation v. Riverkeeper (download PDF:285KB) that EPA may rely on cost-benefit analysis in setting the national performance standards for "cooling water intake structures" that must be upgraded to prevent aquatic plants and animals from being squashed against intake screens (impingement) or sucked into the cooling system (entrainment). This decision is a set back for the environmental activist plaintiffs following a favorable ruling in the Second Circuit Court of Appeals, which held that the language in 33 U. S. C. Section 1326(b) of the Clean Water Act precluded EPA from considering cost when deciding what technology would best minimize environmental impacts. Focusing on the phrase "best technology available for minimizing adverse environmental impact," the majority ruled that under basic Chevron interpretive principles, EPA's decision to consider costs was within the bounds of reasonable interpretation and not categorically forbidden. In reaching its decision, the court noted that: (1) for more than 30 years EPA interpreted Section 1326(b) to permit a comparison of costs and benefits; (2) both respondents and the Second Circuit ultimately conceded that some comparison of costs and benefits is permitted; and (3) respondents conceded that EPA should not have to require industry to spend billions to save one more fish. Had the environmentalists won, EPA could have been forced to require an estimated 554 power plants to retrofit their cooling systems at an estimated cost of $3.5 billion to the electricity industry and their customers.