Police are investigating their second case of vandalism to the NWT's key fibre line in two months, they confirmed on Monday.
Much of Yellowknife and the surrounding area lost access to the internet, with disruption to other services, for much of Monday.
The outage began shortly before 9am, with internet service appearing to be restored for at least some customers shortly after 4pm.
Northwestel said cable home phone, internet, and TV services were disrupted, but did not immediately identify what had caused the outage.
Speaking to Cabin Radio, RCMP spokesperson Marie York-Condon said the outage appeared to be caused by another "deliberate act of vandalism" on the highway between Yellowknife and Behchokǫ̀.
Police had attended the scene of the damage, which was not specified in any more detail, and opened another investigation, York-Condon said.
RCMP are already investigating a similar instance of vandalism that triggered a day-long outage last month.
"The investigation is in its infancy and it is too early to determine if this is related," York-Condon said, reading from a prepared statement.
"RCMP are investigating any potential link."
Police asked anyone who was travelling between Yellowknife and Behchokǫ̀ at around 9am, and who saw anything suspicious – or has dashcam footage – to contact their local detachment.
The full scale of Monday's outage was not easily confirmed. Residents of other NWT communities ranging from Hay River to Fort Smith also reported outages, though Northwestel said that was likely to be only when attempting to access Yellowknife-based services.
In Fort Resolution, Yellowknife, and other communities, residents reported problems using land lines.
Northwestel acknowledged "customers in Yukon, northern BC, Nunavut, and Northwest Territories communities are experiencing intermittent issues with long-distance phone service." The company said local calling within communities was not affected.
"It's brutal, and it's something that we raised with the federal government," Rebecca Alty, Yellowknife's mayor, told Cabin Radio. "They created a whole portfolio recently ... to get more reliable internet to communities across Canada, and we've really been reinforcing the need in the North.
"It's not just, 'Oh shoot, Facebook is down.' It's people's livelihoods. We need something more reliable."
Alty urged residents to ask federal election candidates, when they go door-to-door during this fall's election campaign, what their parties propose to do about Yellowknife's unreliable access to the internet.
There have already been a number of significant disruptions to communications in Yellowknife this year.
Home internet, cable, and mobile data failed on the evening of May 8, then the city and other North Slave communities were left without internet access for most of July 13 following an act of vandalism to the exposed fibre line between Yellowknife and Behchokǫ̀.
On Monday, mobile data, cable, home internet, and land lines all appeared to be affected. Just as in the July outage, on Monday some residents reported intermittent ability to access the internet at very slow speeds while others had no access at all.
Northwestel attributes this to a backup microwave-based internet service which can offer only limited capacity, allowing some connectivity but nowhere near enough for everyone to access the internet as normal.
"People lose the internet at their office but they come here and expect things to work," a frustrated store clerk told Cabin Radio in downtown Yellowknife on Monday morning. Stores were struggling to process electronic transactions and some asked customers to pay by cash only.
At Yellowknife Airport, boarding switched from automated systems to manual checks, though few delays were immediately reported.
Northwestel has remained tight-lipped about the cause of several large-scale outages this year. Police said they are still seeking more information about July's outage, which remains under investigation.