As you embark on your river cruise, do you know the gender of the river?

I sure didn't until cruise manager Mirela Varga said, “The Rhine River is known as Father Rhine. The Moselle River is his daughter.”

Hmm, how does one tell the difference between a boy river and a girl river?

The question of genders of rivers, worldwide led me to search for answers from all sorts of experts, from geographers and cruise guide authors, to linguists and a legendary river explorer. The research was complex and sometimes contradictory. And always fascinating.

As for the Rhine, right off the bat, it showed itself as a muscular guy when I boarded the ship in Basel, Switzerland, where swimmers were getting giddyup rides down the swift currents.

Not surprisingly, the term Rhine comes from the Celtic word renos meaning “raging flow.”

So, are there any basic rules for determining gender?

“Whether a river is known as a he or she depends on its behavior,” notes veteran cruise writer Douglas Ward in his annual books Complete Guide to Cruising & Cruise Ships. For example, says the British author who has been writing the guides for over a quarter century, “the Rhone (in Switzerland and France) is almost always called ‘he' because the waters can be turbulent, bothersome and rough” whereas the Saone (in France) “is a gentler kind of river — more beautiful, more tranquil — and is thus referred to as ‘she'.”

By the time, my cruise had reached the Upper Middle Rhine region in Germany, considered the most scenic part of the river and a UNESCO World Heritage site, the water was calm as a lake. But this section has a reputation.

In days of yore, before modern navigation devices, the narrow section near St. Goarshausen was one of the Rhine's most dangerous, boasting tricky whirlpools and hazardous reefs. Sailors often crashed here. Inspired by these tragedies, German writers penned various legends about a beautiful temptress, Lorelei, whose mesmerizing song distracted boatmen, sending them to their deaths. High above the river, I could see the fabled Lorelei Rock, where the siren is said to sit.

But the Rhine is also considered masculine because it deters invaders. It is a “brother in arms,” I was told by Hans Timmer, a Dutch cruise manager formerly with Uniworld River Cruises. Moreover, it is “a fatherly river (to the Germans) because it protects and is an ally because it is a formidable obstacle to cross and a strong line of defense.”

As my research unfolded, I was learning that the concept of rivers and genders can get very complicated. For example, a single river can be sometimes masculine, sometimes feminine, depending on the country and language. This is the case with the Danube, says Theres Rinner of the Danube Tourist Commission, based in Vienna.

She continues: Whether some rivers are female or male “strongly depends on their history — frequently those rivers' names reach far back into history which makes it hard to track down the exact origin.”

Around the half-way point in my cruise, the ship leaves the Rhine and enters the Moselle River at the strategic 2,000 year-old German town of Koblenz.

According to a book I picked up during a cruise stop, the Moselle has been considered a feminine tributary at least since the 4th century when Roman poet Ausonius called the slim, winding, slow-moving waterway “the most-favored daughter of the Rhine.”

Even the wines from the Rhine and Moselle seem to reflect this male vs female gender difference, according to Kirk Wille, an importer affiliated with Dr. Loosen Wines, an award-winning winery along the Moselle. In an email interview, he said, “Rhine wines, Riseling in particular, are more full-bodied and hearty. Moselle Rieselings are very fine and delicate.”

Well, what about rivers in the U.S.? Unlike German or French, the English language has no masculine or feminine articles, so nouns are neuter. Still, some genderizing seems to be going on, such as in the “Old Man River” nickname of the Mississippi (which, in the Ojibwe language means “big river”). And I'll never forget the song from the musical Show Boat describing the Mississippi as “he just keeps rollin' along.”

If anyone knows about the souls of rivers, it's Richard Bangs, an American and a legendary international river explorer who has authored 19 books, a score of documentaries and over a thousand magazine articles.

When I first contacted Bangs, he emailed that he was in Bosnia, rafting the “female” Una River.

So why is the Una “female?” Because, says Bangs, “it is mostly a lovely, winding, sensual stream.”

Often called the father of modern adventure travel, Bangs later wrote me, “Many (river) names are indeed attributed to gender, often because they remind the explorers or settlers of human characteristics attributed to a gender.”

Bangs went on: “Virtually all rivers were named by men. Very often, if a river is mighty, overpowering, dangerous, it is male,” such as the Tigres, named for the male Tiger. On the other hand, “if it is gentle, curvaceous, easy on the eyes, it is often female.” Take the case of the Mekong, “which means 'mother of all rivers' as it births and feeds many of the great ... waters of China.”

But things aren't always so simple. And Bangs noted, there are no hard-and-fast rules about river names and genders. Names “vary by culture, geography, history, discoverers, and characteristics.” Moreover, he added, “many river names have no gender at all,” such as the mighty Nile, considered the world's longest river, at 4,130 miles.

Susan Farlow is a free-lance writer who specializes in travel stories.