The DFO says conditions on the sea at the time of the grounding were rain, with visibility to about 13km, and winds at 9 knots.
It says the Coast Guard has deployed CCG ships Bartlett and John P. Tully, along with the motor lifeboat Cape St. James.
The Nathan E. Stewart is an Articulated Tug Barge (ATB), a 100 foot vessel that plugs into and pushes a 287 foot barge.
That barge is capable of carrying at least 5.5 million litres (35,000 barrels) of petroleum product, and makes regular trips through the inside passage between the north coast and Metro Vancouver.
The tug was southbound from Alaska when it struck.