Washington, D.C. ? The Supreme Court ruled Wednesday that the government can weigh costs against benefits in deciding whether to order power plants to undertake environmental upgrades that would protect fish.

The court’s 6-3 decision is a defeat for environmentalists who had urged the justices to uphold a favorable federal appeals court ruling that could have required an estimated 554 power plants to install technology that relies on recycled water to cool machinery.

By reducing water intake, the closed-cycle cooling also results in fewer fish being sucked into the system or smashed to death against screens. The Environmental Protection Agency estimates water-intake systems at power plants kill 3.4 billion fish and shellfish each year.

The ruling, written by Justice Antonin Scalia, was a victory for the power industry, which has long advocated for the use of cost-benefit analysis on environmental issues.