A pair of unusually lengthy voyages from American Queen Steamboat Company are going to be the year's hottest river sailing.

"We are practically selling out, and (one is in) August, which is the toughest month to sell," American Queen Steamboat president and COO Ted Sykes told USA TODAY.

The new "Mighty Mississippi" cruises, as they're being called, are 3-week voyages on the 436-passenger American Queen that take in the entire expanse of the Mississippi from its beginnings in Minnesota to New Orleans.

American Queen

The first of the trips kicks off Aug. 14 in Red Wing, Minn. and ends Sept. 5 in New Orleans. The second trip begins Sept. 4 in New Orleans and ends Sept. 26 in Red Wing. Both trips start with a night in a hotel before passengers board the American Queen. They feature more than a dozen stops in such places as Dubuque, Iowa; Hannibal, Mo.; Alton, Ill.; Memphis, Tenn.; Natchez, Miss.; and Baton Rouge, La.

It's the first time in American Queen Steamboat's five-year history that the company has offered such a long trip. Most of the company's voyages are just a week long. Some are even shorter.

"It was (more) luck than judgment,"

said Sykes of winding up with something so popular. While booking data suggested potential interest among customers, he suggested the company didn't expect quite the response it got.

"We saw Europeans that were stitching together two or three cruises to get the entire length of the Mississippi (into one trip), so we put it in for 2016," he said, and then it just "proved hugely popular."

Sykes said one British couple has booked both of the three-week sailings back-to-back, creating a six week Mississippi voyage.

American Queen Steamboat already has added another Mighty Mississippi sailing for August 2017 to meet the demand. Sykes said they would have added even more if it wasn't for a need to get the vessel back to more traditional summer itineraries, too.