A U.S. judge has temporarily blocked a shipment of massive oil field equipment from traversing a scenic Idaho roadway that cuts through the homeland of the Nez Perce Tribe and runs alongside two federally protected rivers.

U.S. District Court Judge B. Lynn Winmill halted next week's planned shipment on U.S. Highway 12 of an oversized water treatment system destined for Canadian oilsands in a decision handed down late Thursday.

He also ordered the U.S. Forest Service to ban the so-called megaload on the 161 kilometres of roadway that crosses national forest lands in Idaho until the agency has conducted a study of environmental, economic and tribal impacts.

The temporary injunction against the shipment of equipment owned by a General Electric Co subsidiary is the latest development in a three-year battle by Native Americans and environmentalists to protect a route in Idaho that follows a historic trail broken by early Nez Perce bison hunters.

Historical route

The route was also used at the dawn of the 19th century by Meriwether Lewis and William Clark on a government-sponsored expedition that charted the newly purchased American West.

The tribe and environmentalists say the winding mountain road that hugs the protected Clearwater and Lochsa rivers should not be turned into an industrial corridor.

But international oil companies see the two-lane highway as the most economical way to transport outsized equipment from the Port of Lewiston in Idaho to the Alberta oilsands.

The fight over the roadway came to a head last month when hundreds of mostly Native American protesters slowed the travel of the first megaload of water treatment equipment owned by Resources Conservation Company International, a subsidiary of General Electric.

General Electric officials couldn't immediately be reached for comment.

The demonstrations came after Idaho granted an Oregon hauler a permit to transport on U.S. Highway 12 the 290,300-kg load that measured 78 metres long, 6.4 metres wide and 7 metres tall. The state did so over the objections of the tribe, environmentalists and the U.S. Forest Service.

But the service ultimately declined to intervene, leading the Nez Perce tribe and conservation group Idaho Rivers United to sue to force the U.S. government to protect the corridor under federal law and through treaty rights held by the tribe.

$5M for GE

At a hearing last week, attorneys for the General Electric affiliate argued that it stood to lose $5 million if its scheduled Sept. 18 shipment was delayed. U.S. Forest Service officials said they wanted to study the issue to prevent harm to either commercial or tribal interests.

In issuing a temporary injunction, Judge Winmill found that the Nez Perce and Idaho Rivers United were likely "to suffer irreparable harm . . . to cultural and intrinsic values that have no price tag" unless the megaload was blocked pending a Forest Service review.

The judge found that General Electric's subsidiary could have avoided any predicted losses had it obtained permission from the U.S. Forest Service - not just Idaho - for its planned shipments.