The 63 passengers and crew aboard the UnCruise Adventures' ship were just three days into their Alaskan vacation when they were informed Wednesday the guest had tested positive and they would have to return to port.
"This was the guest's second test following a negative test result," UnCruise Adventures said in a statement. "The guest is showing no symptoms and no other guests or crew are showing outward symptoms of any kind."
UnCruise Adventures was able to circumvent the U.S. Centers for Disease Control and Prevention no-sail order because its ships carry less than 250 people.
"Social distancing was actually a reality aboard our boat," UnCruise Adventures CEO Captain Dan Blanchard told ABC News, "as well as all the standard things you would think of masks, no buffets, plated meals, separated tables. So we felt, and still do feel, that the actual vessel itself and the way that our trips run, provide a very low opportunity for transmission."
The cruise line has now decided to suspend all future 2020 Alaska departures as the entire industry struggles with how to weather the coronavirus crisis.
"It has affected our life immensely," Blanchard said. "This year we'll have about 2% of our normal revenue and -- and that's devastating."
The CDC's no sail-order expires at the end of September, but major U.S. cruise lines have voluntarily suspended operations until at least the end of October.
"This has been a bit of a come to Jesus moment," Blanchard said, "about how easily even with proper testing, somebody got on board."
Blanchard hopes they can start operations again in the winter in Hawaii, but acknowledged the situation is still very fluid.
"We've been really lobbying Congress for rapid testing," Blanchard said. "That would change the game and would allow sailing before an absolute vaccine."
ABC News' Sam Sweeney and Gio Benitez contributed to this report.
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