Summer ferry service across the Mackenzie River could start later than usual this year, due to low river levels.

The Merv Hardie ferry across the Mackenzie River usually starts in mid-May, but officials warn that it could start later than that. (CBC)

Northwest Territories transportation officials are warning residents not to assume the Merv Hardie ferry at Fort Providence, N.W.T., will start in mid-May as it normally would.

"Every year we have travellers who look at the Mother's Day weekend and the Victoria Day weekend and they start planning their travels for driving out to the south," Transportation Department spokesman Earl Blacklock told CBC News on Thursday.

"This year we want them to be quite a bit more flexible in terms of the planning, so that they have alternatives in case the ferry doesn't come back in as early as it normally does."

The Mackenzie River ice crossing at Fort Providence usually closes to traffic in mid-April. Once the river ice has broken up, the ferry usually starts operating a month later.

But Blacklock said northerners who use the ferry to drive to Alberta — and southern suppliers that transport food, fuel and freight north — may experience a longer cutoff time than normal.

"We want to make sure that they're planning not for the normal period, but rather for a period that extends a week or two at least," he said.

The Transportation Department is also advising motorists to scale back on the use of some roads because of warm spring temperatures.

The winter ice road between Behchoko, Whati and Gameti is being opened to night travel only, while truckers hauling supplies to the diamond mines can drive on the Ingraham Trail only between 10 p.m. and 10 a.m. MT.

"It's meant to protect the surface of the road. The Ingraham Trail is a chip-seal road, [so] it's more susceptible to damage than other highways," said Michael Conway, the department's North Slave regional superintendent.

"So whenever possible, we try to protect that infrastructure so we don't have to spend a whole bunch of money in the springtime rebuilding it or repairing it."

But Conway said this will not impact the diamond mines, since most of their supplies are already on-site.