States Can Mandate Dam Water Levels, Supreme Court Says : Environment: Private hydroelectric plants can be required to permit enough flow for fish and recreation, even if it limits power output, U.S. justices rule.

In a case with far-reaching consequences for all privately owned hydroelectric dams, the Supreme Court ruled 7 to 2 Tuesday that states may require hydroelectric projects to keep enough water in rivers to maintain fish populations, preserve aesthetic qualities and ensure recreational uses.

The case had pitted the state of Washington, which is home to dozens of powerful rivers and even more hydroelectric dams, against Tacoma City Light, a utility company that would own and privately operate a massive water project on the Dosewallops River.

The state had insisted that the utility forfeit some electric generating capacity by leaving the Dosewallops at levels that would allow the continued migration of scarce salmon and trout.

Officials from Tacoma City Light had argued that although states may set standards for water quality, only the federal government, which regulates privately owned hydroelectric dams, may set standards for water quantity.

But Associate Justice Sandra Day O’Connor, writing for the majority, rejected that argument, calling the distinction between the quality and quantity of water in a river “an artificial distinction.”

“In many cases, water quantity is closely related to water quality; a sufficient lowering of the water quantity in a body of water could destroy all of its designated uses, be it for drinking water, recreation, navigation or, as here, as a fishery,” O’Connor wrote for the majority.

Justices Clarence Thomas and Antonin Scalia dissented.

The ruling could affect hundreds of privately owned dams whose licenses are due for renewal in the coming years. Already, operating licenses of about 230 privately owned dams have expired and the facilities are operating pending licensing reviews, and dozens more are due to expire in the next several years.

Among those are nine hydroelectric projects on California rivers, including at least five providing electricity for Southern California.

Environmentalists cheered the ruling, but the hydropower industry said it is likely to create uncertainty over federal licensing of hydropower projects and uncertainty over whether federal or state officials will have the final authority in issuing operating licenses.

“We are very dismayed by the court’s decision,” said Karolyn Wolf, a spokeswoman for the American Hydropower Assn. “It’s left the industry in the lurch and we feel the ramifications for the industry will be severe.”

The ruling also was seen as broadening states’ rights to protect and preserve their waters from degradation by hydropower projects.

Under the federal Clean Water Act, states are responsible for designating uses for streams and rivers, such as for drinking water, fish habitat or whitewater recreation. A state must issue a plan to ensure that those designated uses are not degraded.

Although those plans normally set out complex chemical standards that must be met, the court ruled that states can also enforce standards expressed in more general terms.

In the dispute that prompted Tuesday’s ruling, the state of Washington had designated the Dosewallops as a river capable of supporting the migration of salmon and steelhead trout, species of fish that are considered in danger of extinction. If the Tacoma City hydroelectric plant diverted too much water for power generation, the state argued, the river no longer would be able to meet that objective.

“The ruling shows that water quality and water quantity are strictly intertwined, and have to be treated together under the Clean Water Act,” said Katherine Ransel of American Rivers, a watchdog group that brought the case before the Supreme Court.