Tesla CEO Elon Musk tweeted in late September that an electric pickup truck called Cybertruck, scheduled to begin sales in 2023, “will be waterproof enough to serve briefly as a boat, so it can cross rivers, lakes and even seas that aren’t too choppy.”

Not so fast, said the Washington State Department of Natural Resources, which tweeted a photo of a sinking four-door sedan and warned: “Our derelict vessel crews are begging you to understand that anything that ‘serves briefly as a boat’ should not be used as a boat.”

The tweet-for-tat came at an interesting time in the world of recreational cruising, where shape-shifting designs are no longer the stuff of fantasy. Real, operable amphibious vehicles are now regularly on display at major boat shows, and even the makers of submersibles are touting transformative characteristics that change undersea watercraft into on-the-surface yachts.