It seems like something true cruise enthusiasts could really get onboard with: the marriage of a blue water sailing with one that ventures into the inland waterways.

So, it comes as little surprise that the one company with a solid stake in both the ocean and river markets, Viking, quietly launched itineraries that combine an ocean and river cruise.

Viking currently has three itineraries it calls its Ocean & River Voyages. The 15-day Rhine & Viking Shores & Fjords combines a Rhine river cruise with a North Sea sailing (with both 2018 and 2019 departure dates); the 22-day Grand European & Viking Fjords combines a Danube, Rhine and Main cruise with a North Sea sailing (with departures in 2019); and the 18-day Rhine and Amsterdam to Catalonia brings together a Rhine cruise with a sailing along the Atlantic Ocean (with departures in 2018).

It’s an approach worth watching as a slowly growing number of cruise lines build and offer both ocean and river products. In addition to Viking, Crystal Cruises now has vessels that sail both blue and inland waters, and Scenic is gearing up to make its first foray into ocean cruising with the launch of the 228-passenger Scenic Eclipse this summer.

On a smaller scale, Pandaw River Cruises has started to offer coastal sailings in Southeast Asia in addition to its numerous river cruises on the Mekong and Irrawaddy rivers. Closer to home, American Cruise Lines has cruises both along the U.S. and Canada coastlines as well as on U.S. rivers, and UnCruise offers a Columbia and Snake river sailing in addition to its numerous coastal cruises. French river cruise company CroisiEurope has some coastal ships as well. Since for the most part, river cruises can’t go where ocean cruises can and vice versa, it seems the two would work well together as a combined offering for passengers that have the time and the willingness to experience two very different types of cruising.

Perhaps for Viking, there’s a larger goal at play with the combination cruises, too. Travel Weekly’s cruise editor Tom Stieghorst recently reported that Viking’s senior vice president of marketing Richard Marnell admitted that one of Viking Ocean’s core challenges is that the Viking name is still associated primarily with river cruises. Combining the company’s ocean and river offerings could be seen as a way to introduce those river cruisers to the ocean product.

For companies with access to both markets, the opportunity to cross-market and introduce river cruisers to the oceans and ocean cruisers to the rivers is definitely an advantage worth weighing. While some might argue that they are very different markets with distinct passengers, river cruise line surveys of their passengers often find that many of them are ocean cruisers as well, suggesting that there is a potential marketplace for the ocean-river combination cruise.