Canada is reminding seafarers that smoking marijuana aboard vessels is still illegal despite becoming the second nation to allow recreational use.

Transport Canada has issued a safety bulletin outlining prohibited smoking of marijuana aboard vessels, according to the government's Criminal Code.

"You may not operate, assist in the operation of, or have the care or control of a vessel while impaired," the law states.

"This applies whether or not the vessel is moving."

The new legislation also says that no one may be in any work area whose ability is considered impaired by alcohol or a drug.

"The term "working area" includes anywhere work is being done on a ship and applies to anyone working on a ship in Canada or any Canadian ship outside Canada.

Smoking or vaping cannabis is also prohibited and carrying cannabis across Canada's borders will remain a serious criminal offence, even for medical reasons.

"When considering whether to issue a marine medical certificate to seafarers, Transport Canada and marine medical examiners will consider consumption of cannabis in their determinations," the law states.