Some of the lakes that have been frozen enough for fishing shacks and skating might not be for much longer with a spell of warmer weather this week.

Doug Marlow has been ice fishing at Albro Lake in Dartmouth for more than 35 years and he never gets started without checking the ice first.

Not far from shore, the ice is 19 centimetres -- or seven and a half inches – thick, which is considered safe for walking.

Further out, not so much.

"It's been going down to about three, four, and then re-growing again, so it's been more sporadic with the weather right," Marlow said. "You never know where there may be a hole on the ice, you gotta be really cautious of it."

It's something the Marlows have noticed more often over the years, with fluctuating temperatures a common occurrence during Maritime winters.

Halifax Regional Municipality is advising residents to stay off frozen lakes and ponds, because there's been thin ice and open water spotted in some areas.

Clear ice is the safest kind of ice, says Capt. Barry Bastow of the Halifax Regional Fire & Emergency ice rescue team.

Opaque or "snow ice" is weaker, and grey ice is the most unsafe.

The thick clear ice on First Lake in Lower Sackille was perfect for an ice rescue demo on Monday.

A quick response is the key to preventing hypothermia, Bastow said.

"Hypothermia is not good, it changes your state of mind, you can become confused, and the worst level obviously is unconsciousness, and then you can slip underneath the ice," Bastow said.

Safety tools like ice awls are a must for anyone spending time on frozen waterways.

"You just want to dig in, and pull yourself up out of the ice," Bastow said.