A downed high-voltage transmission line just south of the sewage lagoons in Whitehorse caused more than just a widespread power outage Wednesday evening.

Panic spread quickly after a false rumour started that the Whitehorse Rapids Dam was on the verge of breaking and flooding Riverdale.

"An anonymous woman was cycling by the dam and saw this water coming out then proceeded to go into Riverdale and tell anyone she saw that the dam was going to blow,” Whitehorse RCMP Sgt. Don Rogers told the Star this morning.

But what the woman saw was not a threat to the public.

"During a power outage, our employees are trained to immediately start spilling water under our gates,” said Janet Patterson, the spokeswoman for Yukon Energy.

"Since we're not able to put water through the turbines, we have to spill it.”

If the water is not spilled, it could end up going over the dam, Patterson said.

Power failed just before 8 p.m. to several Yukon communities, including Whitehorse as well as south to Teslin, and north to communities on the Mayo to Dawson City section of the grid. The Minto and Alexco mines were also affected.

The outage was caused by a damaged crossbar on a utility pole, Patterson said.

Police officers went down to the dam to check out the cyclist's claim but didn't think it was an emergency, Rogers said.

However, it was too late to stop the rumour from going viral, especially in the current new age of social media communications.

Between 9 and 10 p.m., the RCMP received 66 calls from the public, including six 911 calls as well as many inquiries from other emergency services.

"There are some suggestions that there were landlords from some apartment buildings going door-to-door telling their tenants to evacuate,” Rogers said.

Social media like Facebook and Twitter also helped spread the rumour, Rogers said.

Some officers were concerned about going into Riverdale out of fear that their presence would start a fresh wave of panic, Rogers said.

Crowds also gathered at the dam to see what was going on.

Officers encouraged people to go home to prevent anyone from getting hurt in the crowd.

Joan Carlson was at home in Riverdale when a neighbour told her there was a crack in the half-century-old dam and it was going to break.

"I tried very hard not to panic but it was very scary,” the 76-year-old said. "But the more people said it, the more I got worried.”

Eventually, Carlson drove up to the Alaska Highway and called 911 before being told that everything was safe.

Even the Yukon Emergency Measures Organization's 24-hour hotline received calls from frightened residents.

Director Michael Tembleton said volunteers who answer the phone were informed of the rumour and were able to calm the handful of callers.

Yukon Electrical Co. Ltd. took so many calls that callers to its after-hours emergency line were put on hold u ntil the next available staff person could speak to them.

Power was restored to Whitehorse by 10 p.m. Some area residents had endured two hours without electricity.