Canadian travellers aboard the Clipper ferry are being warned that smoking marijuana is still illegal, despite recent changes to laws in Washington state.

Clipper Navigation — which operates a private ferry service between Seattle and Victoria, as well as one between Seattle and the San Juan islands — says it has had to put up signs on some its boats after crews caught several passengers smoking pot on board the San Juan ferry.

Clipper CEO Darrell Bryan identifies the culprits as "younger folks that interpreted things to their advantage."

In November 2012, Washington and Colorado legalized the possession of up to an ounce (28.35 grams) of pot by adults over 21, with voters deciding to set up systems of state-licensed growers, processors and sellers.

The measures put state officials in the difficult position of crafting rules for a fledgling industry barred by U.S. federal law for more than seven decades.

Bryan says his ferries are bound by U.S. law, and as such, his crew must report any such illegal activity to U.S. Border Security as well as Seattle police.

Bryan says, while no one has yet been caught smoking pot on the ferry between Victoria and Seattle, signs will likely be posted soon on those ferries as well. just in case anyone gets the wrong idea.

“Why would a Canadian want to come to Washington state to smoke pot when you've got B.C. Bud up there?” he wonders, adding that his bigger challenge is keeping the Clipper loaded with enough alcohol to satisfy Canadians going to Seahawks NFL games.

With files from The Associated Press and the CBC's Lisa Cordasco