An evacuation order was issued for the entire Northwest Territories town of Hay River late on Wednesday as floodwater reached the community's downtown area.
Chief April Martel of the neighbouring Kátł’odeeche First Nation ordered her entire community to leave and head for the community of Enterprise, south of Hay River.
Some 4,000 residents in all are affected.
Residents were told to head for higher ground or to the town's community centre. Yellowknife opened its multiplex as an evacuation centre for people leaving Hay River by road in search of safety.
At the community hall in Enterprise, on the road to Yellowknife, evacuees were told they must register at the multiplex. In Fort Providence, the Big River gas station assisted evacuees through the night. Other residents seemed to be heading for the likes of Fort Smith or northern Alberta.
There were reports of power outages in parts of Hay River as the water rose. Earlier on Wednesday evening, the Department of Infrastructure had declared the only road link to the town's Vale Island impassable, closing it off.
The Town of Hay River asked anyone who has left their home but not yet registered as an evacuee to call 1-833-699-0188.
Mikey McBryan, the general manager of N.W.T. airline Buffalo Airways – which maintains a base in Hay River – said the town's airport, which is on Vale Island, had been shut down.
The first signs of further trouble came earlier on Wednesday evening when a section of ice broke away outside the First Nation and a nearby bridge appeared in danger of flooding. The break sent a fresh surge of water toward Hay River.
Floodwater moved into the downtown with incredible intensity, covering areas in a foot or more of water in minutes. Some residents emerging from hotels and houses already appeared wet up to their knees.
Multiple residents reported being rescued from downtown homes by boat. The Whispering Willows seniors' facility was being evacuated as floodwater reached the rooms.
Sirens rang out across the region. At the First Nation, Chief Martel filmed an entire small home moving along in the floodwater. Other clips showed Martel making a perilous journey by vehicle through several feet of rushing water.
"It's flowing so fast," she said, as floodwater reached the arbour. "The trees are breaking."
The flooding is now unprecedented in scope. Hay River's Old Town areas like Vale Island were long considered to be at risk of flooding, which was one reason for building the newer downtown – this sort of flood was thought highly unlikely in that location.
However, Hay River is essentially a miniature delta through which multiple river channels run, and conditions of the past few days have conspired to create a catastrophe.
Ice jamming those channels has given water nowhere to go, but a weekend of rain and snow in the river's basin has ensured more and more water cascaded into that system.
Hydrometric gauges on the Hay River and its tributaries, some of which are unreliable at this time of year as they can be affected by ice, were showing provisional record water levels long before Wednesday night's flood.
"There was a large volume of ice, a large volume of snow in the basin over winter, and then this storm hitt – initially as rain, which then flowed directly into streams and creeks, bumping up the water level immediately – and it parked over the entire basin," GNWT hydrologist Shawne Kokelj said earlier this week.
"Now what we're seeing is there's still high water coming from farther upstream because a lot of rain fell there, too, and now some of the snow is melting and so keeps feeding a lot of these smaller streams.
"As soon as you stop a river, the volume of water seems incredibly large and it backs up quickly."
United Way N.W.T. is taking donations for those affected by the flooding. The Northwest Territories government has pledged to match up to $150,000 in donations.
Ollie Williams and Caitrin Pilkington, Local Journalism Initiative Reporter, Cabin Radio