Up well before the crack of dawn, they aim to hit the water by 5 a.m. Only this month, there’s been no water to hit.

The Toronto Fire Service’s Marine Unit has what could be considered the city’s coldest job, casting off each frigid morning in their icebreaker to clear a cross-hatch of channels through the frozen harbour.

“It’s definitely negative 40 out there. I don’t care what the radio says,” quips firefighter Geoff Woodmansey.

Their daily sorties are an important part of emergency preparedness, says Fire Captain Michael Hagarty, who heads up one of the four shifts that crew the boat. From the industrial Port Lands to the island airport, “it makes everything accessible,” he says.

Last week, ferries to the Toronto Island stopped running due to thick ice, but the Billy Bishop Airport ferry still runs between 5 a.m. and 11 p.m.

“After 11, that ferry shuts down and we’re it,” Hagarty said.

While the winters of 2012 and 2013 were completely ice-free, the past two have brought more ice-up than anyone’s seen in a long time. The harbour was frozen solid from the island to the city for more than a month last winter, and this year the firefighters say the ice is even thicker.

The William Lyon Mackenzie, a 24.7-metre steel fire tug named after the “firebrand” leader of the 1837 Rebellion, operates year-round. Purpose-built in Owen Sound in 1964 to replace the wooden ship used at the time, the “WLM” is a multi-purpose rescue boat/pumper/ice breaker. It carries almost a mile of hose on board and can pump lake water to douse flames anywhere in its area of responsibility, from Etobicoke Creek to the Rouge River, extending five miles out into the lake.

While the crew says summers are much busier, filled with search-and-rescue operations and even the occasional spill containment, the winters provide long, lonely weeks, where the only living beings encountered are the ducks and gulls that haven’t migrated south.

The firefighters are constantly on call for rescues should anyone go through the ice, but joke that the only rescues they’ve done this season were for ducks and swans frozen to the ice.

“We use a little hot water to thaw them out,” laughs Woodmansey.

Crewed by two mariners (a captain and an engineer) and five firefighters (a fire captain and a four-person pumper crew), the WMH added four extra “souls” for its morning sortie on Tuesday (a pair of Star journalists and a CBC news team).

After revving up the twin 600-horsepower engines, the WLM growls away from its slip near the foot of Bathurst St. and imposes itself on the thin layer of ice that’s formed since it last left. Cracks fire out from the bow of the ship, snaking through the previously broken ice.

A few hundred metres out, the broken glass sound gives way to a deeper groaning and we slow as the thicker ice starts to have its way with us. The boat is tossed from side to side, ricocheting off plates of ice more than 20 cm thick to find the path of least resistance.

As we approach the Royal Canadian Yacht Club — a large wooden building shut for the winter, but considered a fire risk — the scraping of ice on the hull takes on a strange metallic edge, like crunching ice cubes between your fillings.

While the WLM isn’t a true icebreaker, it was designed to operate in winter conditions and is considered an “Ice Class One” ship. When it encounters ice too thick to push through, it rides up on top of the sheet and uses the weight of the boat to snap it in half. The shards of ice — as big as small cars — rise up on both sides of the boat like mini-tectonic plates, and one has the impression of watching mountain ranges form in fast-forward.

As we approach the RCYC the boat grinds to a halt and the engine cuts. Has the ice won? Ship’s Captain Tito DeConcilys shifts into reverse and then accelerates to get a running start at the stubborn ice, driving the bow up and breaking through once more.

The fire boat heads next to Hanlan’s Point, then across to the industrial area at Pier 51, where two Great Lakes cargo ships — or “lakers” — are overwintering. Retracing the same routes day after day, tracing red lines on the GPS screen in the wheelhouse, the fireboat will take more than two hours to complete its task.

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And with temperatures that frequently dip below -30C, DeConcilys says the passages will ice up again in a matter of hours.

“The thing is, we’ll go back out tomorrow and it’ll be just as tough.”

More: The chilling details of a cold water rescue

Do you work a job that could be considered Toronto’s coldest? Contact Marco Chown Oved at 416-869-4892 or moved@thestar.ca