Sainte-Marthe is built on a lake bed. How did that happen?

Like many of the suburbs that dot Montreal's North Shore, Sainte-Marthe-sur-le-Lac was home only to summer cottages not so long ago.

The area routinely flooded when the Lake of Two Mountains swelled in the spring.

Then a dike — a grassy knoll packed with gravel and earth — was built in 1980.

With the dike's construction, the municipality grew, as it allowed more people to build year-round homes closer to the lake.

The town's logo even pays homage to the dike, represented as a swerving blue line separating "firm ground" from the Lake of Two Mountains.

With low taxes, waterfront views and its proximity to the city, Sainte-Marthe has grown rapidly, its population more than doubling from 8,300 in 1995 to 18,000 in 2016.

But since the dike burst Saturday — forcing thousands from their homes — there have been questions about a lack of government oversight and whether authorities should have acted more quickly in improving the structure.

The dike was inspected after the historic flooding two years ago, and plans were in place to repair it this fall.

But the disastrous breach has prompted broader concerns about how municipalities in the Montreal area have allowed their waterfronts to be developed.

'There is a nonsense there'

In Sainte-Marthe, the construction of the dike allowed much of the town to be built, effectively, on the actual lake bed.

"I think the focus and the question is, what kind of circumstances over the last several decades led to large urban areas completely [dependent] on a system of dikes," François Brissette, a hydrologist and professor at the École de Technologie Supérieure, told CBC Montreal's Daybreak.

"There is a nonsense there. And that's the key problem that should be looked at."

Brissette said proper bylaws and regulations would have prevented people from building homes on flood plains.

"There would have never been a need for those dikes, and there would have never been dike failures, and there would have never been all the problems we are witnessing now," he said.

The lure of property taxes

Municipalities' dependence on property tax revenues has driven the expansion onto their waterfronts.

"For them, the house with the nice view of the river brings a lot of taxes. And if they want to develop a new library or whatever plan they have, they need money," said Pascale Biron, a professor of geography, planning and environment at Concordia University.

Biron said decisions about zoning and flooding mitigation measures should be made at the provincial level, taking into account the full impact of those decisions on the watershed.

In the spring, the rain and snowmelt has to go somewhere, she explained.

"You need an overall approach," she said.

"If you put levees and dikes everywhere, the risk might be that water is routed faster downstream."

A river needs to breathe

Experts point to European countries, like the Netherlands, where authorities have stopped building up dikes and, instead, moved them back, to allow the river to "breathe" during the spring runoff.

Martine Chatelain, a spokesperson for the environmental group Eau Secours, said although Quebecers have a strong connection to the water, it may be time to rethink the assumption we should live right next to it.

"It's beautiful, that's true," said Chatelain, who grew up on a lake in the Laurentians. "But it doesn't always make sense."

When asked Wednesday whether the government plans to allow the reconstruction of the dike in Sainte-Marthe-sur-le-Lac, Quebec Premier François Legault said no decision has yet been made.

"Do we have to build all of it, a part of it? It will have to be studied," he said.

Legault said he wants to have a broader look at what's defined as a flood zone.

"It's not an easy process to redefine a flood zone, but I think it's important that we do so.

"With what happened in 2017 and this year, it's clear that we're in for a new impact with what's happening every spring."