STEUBENVILLE, OHIO, JAN. 8 -- A six-day-old oil slick came to a standstill outside this Ohio River city today, forcing businesses to close and drying up water taps in thousands of homes.

"We've got big-time water problems," said city council member Tina Gump. "The river is not moving. The oil slick is stationary, and it's smack on top of our intake valve."

Thirty miles downstream, authorities in Wheeling, W.Va., shut off the city's main water intake after detecting a "strong odor" of diesel fuel, and city officials crossed their fingers that a makeshift water delivery system would keep the city running.

Local authorities say a temporary pipeline will provide about 75 percent of usual water needs. But City Manager Michael Nau said he would not hesitate to close nonessential businesses or take other measures.

"That spill is massive," Nau said. Wheeling uses about 9 million gallons of water a day and the makeshift system is expected to supply more than 5 million gallons.

More than a million gallons of No. 2 diesel fuel spilled into the Monongahela River last Saturday near Pittsburgh when an Ashland Oil Co. tank collapsed. The spill rapidly made its way into the Ohio, where it curtailed water supplies for 750,000 residents of Pennsylvania and is threatening thousands more in Ohio and West Virginia.

Federal and state officials had hoped the slick, now nearly 100 miles long, would slide by quickly, forcing only brief interruptions in water service.

But bitter cold and icing have slowed the river to a crawl, and the heaviest concentration of fuel is lingering near Steubenville.

Only food stores, filling stations, drug stores and medical facilities were allowed to open in the community of 50,000.

"Last night you could have put a cork out there in the water and it wouldn't have moved," said Ohio Environmental Protection Agency spokesman Al Franks. "The water is mostly oil, all the way to the bottom."

In an effort to dislodge the oily mass, the Army Corp of Engineers has released extra water from the New Cumberland, W.Va., Dam north of town.

"It's trying to move a little bit," Franks said. But progress of the spill is being measured in feet per hour, he said. "It might be days even weeks, before the entire mass is gone."

Steubenville officials had hoped to keep their water system in operation by using a special cleansing technique. The system had been used successfully upriver in East Liverpool, Ohio.

City manager Bruce Williams said the plan was abandoned after technicians sampled water over the main intake valve.

"We can't treat almost pure diesel oil," he said.

Part of the problem is that diesel-contaminated water can foul water treatment systems and pipes, requiring the replacement of a expensive filters and settling basins and perhaps leaving water supplies with a permanent flavor and odor.

"It's horribly hard to clean," Franks said.

Ohio Lt. Gov. Paul Leonard, in Steubenville, predicted that "problems will be with us for 30 to 40 days" as traces of the slick make their way to the Mississippi River and possibly the Gulf of Mexico.

"It will take a long time before people feel confident about their drinking water," he said.

Steubenville cut off its intake Wednesday, expecting to weather the water crisis with the help of 1 million gallons stored in two municipal swimming pools. The city normally uses 6 million gallons a day.

Instead, Gump and other officials were on the telephone today, lining up tanker trucks, soothing businessmen and urging residents to think dry.

"Schools are closed. Churches are closed. Social gatherings have been ordered not to happen," Gump said. "We don't know how long we'll have to survive it."

In Wheeling, truckloads of bottled and canned water are at the ready, courtesy of the Anheuser Busch and Miller brewing companies, and tanks of water have been shipped in from as far away as Wisconsin.

Cincinnati officials anticipate the oil will reach that city's water intakes by Feb. 1, but they said they expect to have four or five days of water stored by then.

Coast Guard supervisors predicted that all recoverable oil could be removed from the rivers in the Pittsburgh area by Monday unless temperatures drop or snow intensifies. Much of the million-gallon spill has mixed into the water beyond the reach of vacuum hoses and skimming barges, Petty Officer Dean Jones said. As the oil descends the river -- it reached 105 miles from its origin today -- it dilutes, reducing its toxicity, he said.

At least 8,000 suburban Pittsburgh residents remained without water today.

Staff writer Michael Weisskopf contributed to this report.