It’s hell on the high seas.

Cruise liners experienced an unprecedented crime wave this summer, with 35 sex assaults, two disappearances and five thefts of $10,000-plus reported to the FBI during the third quarter of this year.

The agency fielded more complaints of serious crimes on cruises from July through September than during any other three-month period since at least 2016, the most recent year for which data is publicly available, according to the US Department of Transportation’s most recent Cruise Line Incident Report published last week.

Sex assaults were by far the most frequently reported crime.

Of the 35 reported sexual assaults, 27 involved passengers; five involved crew members and three cases involved “others” — though the FBI would not specify whether that breakdown addressed victims or perpetrators.

The sexual assaults were widespread, reported on ships owned by six different cruise companies, including family-oriented Disney — from July 1 through Sept. 30. That’s a 35 percent uptick in sex assaults from the previous quarter, and a 67 percent increase from the same time period in 2018.

Sex assault cases formed the bulk of the 46 total crimes reported.

Overall, crime spiked 44 percent from both the previous quarter and from the third quarter of 2018, when there were 32 alleged incidents during each time frame.

In recent years, cruises-in-chaos have become viral social media moments and major national news stories — from tragedies like the July death of an Indiana toddler whose grandfather accidentally dropped her into the Caribbean, to violence and plain stupidity, like the woman caught balancing on the edge of a Royal Caribbean boat’s balcony in October while posing for Instagram.

Cruises are more popular than ever, with 14.2 million North Americans setting sail in 2018, a 9 percent increase from the previous year, according to Cruise Lines International Association.

Six of the 12 cruise lines monitored by the FBI saw no serious crimes, according to the third quarter report.

The companies are required by the Cruise Vessel Security and Safety Act to report alleged homicides, suspicious deaths, missing persons, assaults with serious injuries, theft over $10,000, and incidents of people tampering with the ship to the agency.

There were no homicides and no suspicious deaths reported.

Carnival Cruises, the world’s largest cruise company, reported the most incidents with 28, including 20 sex assaults; two missing people; two serious assaults and two thefts. That marks a 47 percent uptick from the same quarter last year, when there were 19 reported Carnival incidents.

Carnival’s 25 ships take 1,500 voyages each year.

The two missing persons were “intentional man over boards” who couldn’t be saved, Carnival claimed.

The cruise company was among the three to dock their ships in New York City during the third quarter. Carnival, Disney and Norwegian made 60 “calls” to the Manhattan Cruise Terminal along the Hudson River, delivering a total of 322,000 passengers to the Big Apple, according to the New York City Economic Development Corporation, which manages the terminals.

The Brooklyn Cruise Terminal in Red Hook took 14 calls from Carnival cruises carrying a combined 73,000 passengers.

Passengers spend hundreds of millions of dollars in the Big Apple each year, the city has said.

Royal Caribbean, the world’s second largest cruise company, had 11 alleged serious criminal incidents during the reporting period: eight sex assaults and three thefts — a 267 percent uptick from the third quarter of 2018, when there were just three serious crimes reported.

The company said in a statement that “the safety and security of our guests is our top priority, and we take every allegation of wrongdoing seriously,” adding that it offers “extensive security” and sexual-assault-victims-assistance training for employees, in addition to counseling for “guests or crew in need of support.”

Chloe Wiegand, the toddler who fell from the 11th-floor balcony of the Royal Caribbean’s Freedom of the Seas, was among the late-summer cruise victims.

In a heart-wrenching new interview, the grandfather said “I kind of relive it all the time, and I just thought there was glass there,” Salvatore Anello told CBS This Morning in his first public interview last week.

Prosecutors in San Juan, where the ship was docked when Wiegand died, have charged Anello with negligent homicide. It’s unclear if the death is included in the latest Incident Report. The US DOT and Coast Guard did not respond to requests for comment, and the FBI declined to comment on Wiegand’s death or any other ongoing investigations.

In addition to Royal Caribbean and Carnival, Norwegian, Disney, Celebrity and MSC Cruises also reported incidents during the reporting period (see graphic).

Six cruise lines reported the following crimes to the FBI from July through September 2019*

Carnival

Missing people: 2 | Sexual assaults: 20 | Assault with serious bodily injury: 2 | Theft of more than $10,000: 2 | Tampering with vessel: 2

Royal Caribbean

Sexual assaults: 8 | Theft of more than $10,000: 3

Norwegian

Sexual assaults: 3

Disney

Sexual assaults: 2

Celebrity

Sexual assaults: 1

MSC

Sexual assaults: 1