The electrical failure — the worst in North America's history — began when a tree branch touched a power line in Ohio and then spread through eight U.S. states and Ontario, affecting more than 50 million people. Some cities did not get their power restored for four days.
"The blackout really tested the system," said Ontario Energy Minister Bob Chiarelli, who was mayor of Ottawa at the time.
He said Ontario's aging electrical system was "very, very weak."
"We had a deficit of electricity, we were importing on a regular basis and we had actually lost generation in the province of Ontario because of lack of investment. The transmission system had been leaking, we had less capacity in transmission because of a lack of investment by previous governments."
The situation wasn't much better south of the border.
Industry leaders had been calling for years for the mandatory implementation of industry standards across the continent, which experts say could have prevented the blackout.
"It's one of the major changes that came out of the 2003 event," said Gerry Cauley, CEO of the North American Electric Reliability Corporation (NERC).
"There had been discussions before as early as the mid to late 90s about the need for mandatory reliability standards, but it really never got over the finish line."
Cauley said it took two more years before the U.S. Congress passed the Energy Policy Act, which gave the Federal Energy Regulatory Commission authority over grid reliability and the hammer of potential civil penalties and fines up to $1 million a day.
FirstEnergy Corp., the Ohio-based company at the heart of the power outage, went to great lengths to update their capabilities to prevent a similar disaster from happening again.
"We've added new facilities, new equipment, we've enhanced our operator training and implemented new NERC operational standards and the key piece is they are now mandatory and enforceable," said company spokesman Mark Durbin.
"We believe that's helped enhance the reliability of not just our piece of the transmission system, but of the transmission system as a whole."
But despite the improvements, industry experts and government officials agree that the grid now faces more threats than it did in 2003.
"One of the highest priorities of NERC today is cyber security and severe weather events ... they're priority areas but I don't think there's 100 per cent comfort in the system yet in those areas," said Chiarelli.
"We see foreign countries invading the cyber security system of embassies in different countries and it's that type of cyber security that is also a risk to the energy system," he said.
"So they're upgrading the cyber security on an ongoing basis to ensure that that doesn't happen."
Ontario's energy watchdog said the grid's susceptibility to these threats grew in the years following the blackout.
"Cyber threats are becoming more and more of an issue... they probably escalated in the last five or six years from where they were in the last seven or eight years, but then so has our readiness," said Kim Warren, vice-president of operations of Ontario's Independent Electricity System Operator.
"You never say never in this line of business, but things are significantly enhanced from where we were in 2003 ... the types of things that we do try to balance the risk against these extreme type of events and the costs of increasing readiness."
Some U.S. politicians initially said the power outage originated in Canada. That did not sit well with then Toronto mayor Mel Lastman.
"All I heard was the Americans blaming it on us, and I made a statement where I said 'the Americans are always blaming it on Canada,' and that went right across the United States," he said.
"It was crazy, they didn't know anything, we didn't know anything — it was too early to know whose fault it was and there they were blaming it on us."
Although terrorism was an early focus of the joint U.S.-Canadian task force that investigated the cause of the blackout in the following months, it was soon dismissed as the cause of the blackout.
Ten years later, it is much more of a concern.
"I think we're in a whole new ball game now with all the terrorism aspects ... I'm not up to date on all of the precautions and measures that are being taken to try and protect against that, but it's certainly a much bigger concern than it was even then," said former Ontario Premier Ernie Eves.
Ontario's power grid has undergone many improvements in the last decade.
An executive at Hydro One said the possibility of a similar event occurring today is low but unpredictable human error could lead to problems across the grid again.
"From the lessons learned we are in a better position to restore the system in a more efficient and perhaps quicker manner," said Bing Young, the company's director of transmission system development.
"But if there are jurisdictions out there south of us that have not been complying with the standards and have allowed situations to occur ... that's not entirely within our control."
For many Ontarians, Aug. 14, 2003, is the day when they pulled together.
"People were celebrating, they really did, there were barbecues in the backyards and they invited all their neighbours," Lastman said.
"I was concerned about what could happen — the looting and break-ins — but there wasn't anything happening."
Peter Carayiannis, a Toronto lawyer who helped direct traffic for four hours on the day of the blackout, said the fact that there was no increase in crime "was a testament to the citizens of Toronto."
"We really banded together, there were street parties ... restaurants were offering their food at a discount or for free and I think all the ice cream places gave everybody a free cone that day," he said.
"So it was really a sense that people wanted to make the best of a situation, we were all in it together and if we co-operated and just took care of our brothers and sisters that we would get through it and everybody would get home safely."