The U.S. Supreme Court will decide whether to switch gears on more than 30 years of regulating the muddy water running off logging roads into rivers.

At issue: Should the U.S. Environmental Protection Agency keep considering it the same as water running off a farm field, or start looking at it like a pipe coming out of a factory?

The case being heard Monday in Washington, D.C., was originated by a small environmental group in Portland, the Northwest Environmental Defense Center.

It sued the Oregon Department of Forestry over roads on the Tillamook State Forest that drain into salmon streams. The lawsuit argued that the Clean Water Act specifically says water running through the kinds of ditches and culverts built to handle storm water runoff from logging roads is a point source of pollution when it flows directly into a river, and requires the same sort of permit that a factory needs.

"We brought this out of a perceived sense of unfairness," said Mark Riskedahl, director of the center. "Every other industrial sector across the country had to get this sort of permit for stormwater discharge," and the process has been very effective at reducing pollution.

The pollution running off logging roads, most of them gravel or dirt, is primarily muddy water stirred up by trucks. Experts have long identified sediment dumped in streams as harmful to salmon and other fish.

The center lost in U.S. District Court in Portland, but won in the 9th U.S. Circuit Court of Appeals in San Francisco. The Oregon Department of Forestry and Georgia Pacific-West appealed to the Supreme Court, and 31 states threw in with them.