As long as water conditions allow for a safe landing. In much of the world that severely limits when you can operate due to storms or ice. In practice routine use of ground effect vehicles will be mostly limited to lakes and inland seas with fairly benign weather. Like I don't think we're going to have regular passenger service from San Francisco to Los Angeles or Detroit to Cleveland.
Ground effect planes are already pretty limited to calm water situations. Like between Seattle and Victoria, or maybe Seattle and Vancouver. I would say the Alaskan marine highway would be a good fit, but that is mostly for freight and cars.
