A sunny break from heavy wind and rain allowed crews to come out in force to battle an oil spill that has stained one of Alberta's most important rivers – one that, environment officials warn, is likely to never be completely cleaned up.

Rough weekend weather and a flooded Red Deer River had impeded efforts to clean up a spill of 160,000 to 480,000 litres from a Plains Midstream Canada pipeline. But on Tuesday, a response team of nearly 200 workers set to work skimming, vacuuming and absorbing the spill.

It was difficult work, made worse by the high water that is hampering access to the 25 pools of oil that Plains crews have identified in back eddies along the 30 kilometres of river that stretch between the ruptured pipe and Lake Gleniffer, a reservoir whose dam has helped contain the spill.

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"It's been very, very difficult to access a lot of these areas because of the high flows, the very rapid current," said Martin Bundred, the lead man on the spill for Alberta Environment and Sustainable Resources Development. "We have to use airboats to get in [and there are] lots of sandbars lots of obstacles – whole trees coming down the river. It's not a nice place to be."

In fact, the challenges of cleaning an oil-stained river are so great that it's unlikely that all of the oil will be cleaned up. Some will deliberately be left alone to degrade naturally, an unwelcome prospect for those whose backyards and pasture lands along the Red Deer have been blackened from the leak.

"There are situations where it does make sense to leave things in place," said Mr. Bundred. In this case, "with a very light crude, you're going to get degradation very quickly."

Even light crude can take a long time to disappear, however. Last July, another pipeline ruptured below a river, spilling 240,000 litres of light oil into the Yellowstone River from a pipe owned by ExxonMobil, an accident that carries numerous echoes of the current Alberta situation. At one point, 1,000 people were involved in attempting to clean up the Yellowstone, in an effort that cost Exxon $135-million (U.S.).

But they could only do so much. In some areas, officials determined that it would do more harm to get to the oil – through building roads and driving in heavy equipment – than to simply leave it.

"We call it natural attenuation, which is a technical term for leaving the damn stuff in place," said Richard Opper, director of the Montana Department of Environmental Quality. "We figure it will be gone in probably about three, at the most five, years."

The Alberta effort will be aided, however, by the collection of oil in Lake Gleniffer, which has prevented the crude from spreading further downriver and tarnishing drinking water supplies for Red Deer, Alberta's third-largest city. Plains has tested water at 18 locations twice daily. It says only one test failed, at one location on the first day. The company also promised compensation, as it prepared to vacuum any oil remaining from the leaking pipe below the river, a process that could take a week.

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"To the extent we have impacted residents, we are going to make it right," said Stephen Bart, vice-president of crude oil operations for Plains.

But the notion that parts of the spill may never be cleaned up is little solace for those most affected. The province has said the river should flush away most of the ill effects, and return to a healthy state soon. Those who have seen the oil aren't convinced.

"This could kill the Red Deer River," said Lorraine Mikal, whose family farms land along the river, and owns 1.5 kilometres of waterfront. She said she worries about "the long-term health effects."

Even seeing trucks vacuuming oil from standing water near her house this week did little to reassure Bonnie Johnston, who has seen oil matted in grasses and woody debris across her 57-acre property. Worse, her home draws water from a well that she now fears is contaminated.

"This place is worthless if you have no water," she said. "I don't believe it can ever be used again."