Cruise lines have yet to officially cancel Alaska sailings for 2021, even though a cruise ship ban announced last week by Canada will make most of them unviable.

But in recent days, they have begun making the trips unbookable at their websites — or removing them from the websites completely.

Alaska sailings scheduled for 2021 have become unbookable since last week at the websites of five of the six big-ship lines that operate in the state Princess Cruises, Holland America, Royal Caribbean, Carnival Cruise Line and Celebrity Cruises.

The exception is Norwegian Cruise Line, which continues to show 2021 Alaska sailings as bookable on its website.

Scheduled to remain in effect through Feb. 28, 2022, the new Canada cruise ban will more or less end the Alaska cruise season before it begins, as most cruise ships must make a stop in Canada during Alaska cruises for regulatory reasons.

Most cruise ships are flagged outside of the United States, and by law such vessels cannot cruise in American waters without stopping at least once per voyage at a foreign port. On a practical level, that means the Alaska cruises offered by most lines must include a stop in Canada.

Unless Congress passes a waiver to the 135-year-old law, the Passenger Vessel Services Act and President Joe Biden signs it, or Canada’s new cruise ban is rescinded, there will be no cruising in Alaska this year for most ships.

Every line that’s stopped taking bookings for 2021 Alaska cruises on its website has handled the situation a little differently. At the websites of Royal Caribbean, Celebrity and Holland America, 2021 sailings to Alaska have disappeared completely. A search for Alaska cruises only turns up sailings scheduled for 2022.

At the Princess website, a search for 2021 Alaska cruises still turns up the voyages the line had planned for the year, with all of the normal details about scheduled port calls, shore excursions and the onboard experience. But each of the sailings now has a notice saying it is “currently not available.”

A search for 2021 cruises to Alaska at the Carnival website simply turns up a full-screen message that says “Oh Snap! There aren’t any cruises with the details you searched for.”

The one outlier among the big-ship lines, Norwegian, is continuing to take bookings as it studies the implications of the Canada ban and its options, the line has said.

“We are currently exploring several initiatives that may allow such cruises to continue, especially for the important Alaska season,” the line said last week in a statement. “Given the fluidity of the current environment, we will also continue to work with the Canadian government to amend their current suspension.”

Norwegian’s two smaller sister lines, Regent Seven Seas Cruises and Oceania Cruises also continue to show Alaska sailings for 2021 as bookable on their websites.