CALGARY, Canada  — Power outages in the Canadian oil capital of Calgary could last for weeks or even months, city authorities said on Sunday, after record-breaking floods that killed three people and forced more than 100,000 to flee their homes swept across southern Alberta.

Some Calgary residents were able to return to sodden homes as river levels slowly dropped and some mandatory evacuations orders were lifted.

But Bruce Burrell, director of the Calgary Emergency Management Agency, said power restoration in the downtown core, where many of Canada's oil companies have their headquarters, could take days, weeks or even months.

Many of oil companies were making plans for employees to work from home.

"This is an evolving situation and because of the volatility of electricity and water and the infrastructure that was damaged we have got a lot of issues with restoring power to different parts of the city of Calgary," Alderman John Mar told CBC radio.

"We are facing an absolutely gargantuan task."

Heavy rains were blamed for 750 barrels of synthetic oil spilling from a pipeline approximately 43 miles south of Fort McMurray in northern Alberta early on Saturday.

"We are still investigating the cause, however, we believe that unusually heavy rains in the area may have resulted in ground movement on the right-of way that may have impacted the pipeline," Enbridge, Canada's largest pipeline company, said in an emailed statement.

The company also has shut down two major oil pipelines serving Canada's oil sands region as a precaution.

Provincial authorities said it was too early to count the cost of the flood damage because rivers have not peaked in some places.

The South Saskatchewan River is expected to burst its banks in the city of Medicine Hat in southeastern Alberta on Monday. About 10,000 people have been evacuated.

The floods already look significantly worse than those of 2005, which caused $383 million in damage in the western Canadian province.

The floods followed 36 hours of unusually heavy rainfall that pushed the volume of water in rivers to record levels. Some communities received six months of their normal rainfall in fewer than two days.

Evacuations started on Thursday and utility Enmax switched off power to central Calgary on Friday afternoon to avoid water damage to its downtown facilities. Troops were used on Sunday morning to shore up the east bank of the Bow River in Calgary and ensure the stability of an Enmax substation.

It was unclear how much crude trading would take place on Monday after little if any trade on Friday.

Shorcan Energy Brokers, which provides live prices for many Canadian crude grades, operated out of Toronto on Friday rather than from Calgary, although there were no trades in Western Canada Select heavy blend or light synthetic crude.

Net Energy Inc, the other main Calgary crude broker, was closed on Friday and no trading took place.

As the Bow and Elbow rivers in Calgary, which during the weekend hit five times their normal flow rate, slowly receded, the scale of the damage became apparent. Roads and pavements were left covered with a layer of thick silt, fallen trees lined the riverbanks and residents pumped dirty brown water out of basements.

Police said three bodies had been found near High River, about 60 km (40 miles) south of Calgary.

Flood water covered the grounds of the Calgary Stampede, an annual extravaganza of cows, cowboys and horses scheduled to start on July 5. City authorities insisted the show would go ahead despite the disruption.