The water barrelled down the slope of Mount Royal, with some people struggling to avoid being swept away by the mighty current.
The flood began spreading near McGill University just before rush hour, prompting traffic jams as police rerouted cars and people struggled to escape the area.
Some people wrapped themselves in garbage bags to protect their lower body from the ice-cold water as they crossed submerged streets.
At one intersection, where the flooded area was narrow, people moved a sidewalk bench and used it as a bridge to get to the middle of the street.
Philippe Whitford, a 38-year-old program analyst, gave new meaning to the term double-bagging: he wrapped himself in two layers of green plastic bags and made his way through the knee-deep water outside his building.
While he felt cold — the temperature was -9 C — he was grateful that he managed to stay dry.
His concerns quickly shifted to Tuesday morning. As the break was contained by mid-evening, and the water was largely cleared away, an emerging problem was ice buildup.
With a slippery film quickly forming across the area, parts of Ste-Catherine Street risk being temporarily transformed into an urban skating rink.
"It's going to be a mess when this all freezes," Whitford, who works for a finance company, said of Tuesday's commute.
The streets thickened with ice as firemen stabbed at drain openings with pike poles to get the water to go in. There were also large road graders pushing the water around trying to get it to disperse.
City officials said the flood was caused by a 90-centimetre water main that broke at a construction site near downtown, and said they were working to fix the problem.
Police rerouted traffic because the cascade of water made the area extremely slippery as it turned to ice. Parts of two of Montreal's main east-west arteries were closed to traffic — Rene-Levesque Boulevard and Sherbrooke Street.
Staff at McGill University were warned that several of the university's buildings were flooded and evening classes were cancelled.
Water also trickled into a number of commercial establishments on Ste-Catherine Street.
City officials said the incident had not affected the quality of drinking water.
Mayor Michael Applebaum went to survey the cleanup operation.
He said the damage occurred mostly below street level.
A steady stream of water poured into underground parking garages, and Applebaum said water had to be pumped out of the Place Ville Marie, a major office complex.
"The damage is mostly damage where we have basements where there's underground parking lots," he said as he stood near a water-logged intersection, as firefighters cleared clogged sewers and front-end loaders scooped up water.
Two minor injuries were reported, as of 7 p.m. The local ambulance service said the injuries occurred when people slipped and fell.
One man who was rushing to catch a bus said he saw the cascading water push people along as they waded through.
Another man, Faz Khan, said he watched the spectacle from his office window.
"McTavish (Street) was completely flooded and nobody could cross past Sherbrooke," Khan said. "People had water up to their knees at one point.... It was pretty bad."
Also on HuffPost