Ketamine users are taking to the sea to avoid detection following police success at flushing out party venues on land.
Marine police detained 59 people aged 15 to 53 and seized 32.3 grams of the drug after intercepting three pleasure boats in three separate cases in the past four weeks.
Superintendent Albert Ho Wai-hong from the marine police regional crime unit said the number of arrests at floating drug parties had risen this year. But there was no evidence yet that the parties were being organised through social networking sites.
"Investigation indicated they learned of the parties from their friends," he said.
A veteran officer said organising drug parties at sea made it easier to avoid detection. "They can throw their drugs into the sea before officers go on board their boat to check."
Marine police have stepped up checks at public piers, particularly Sai Kung's, and on boats at sea.
On April 29, a small quantity of ketamine was found on the body of a man, 25, who died after falling into the sea from a yacht off Sai Kung.
Ho said the arrest of 28 men and 31 women on the three boats was part of the annual "Thunderbolt 12" operation to crack down on the triads and organised gangs in Hong Kong, Macau and Guangdong.
The operation, which began on July 9 and ended on Wednesday last week, was a joint effort with police in Macau and Guangdong. "We have been offering assistance to each other," said Chief Superintendent Kwok Ho-fai of the Hong Kong police organised crime and triad bureau.
Hong Kong police arrested 1,191 people during a city-wide search of 1,680 locations, including pubs, gambling and vice dens, massage parlours and flats. Officers seized HK$8.9 million in cash and illicit goods, including drugs, contraband cigarettes, illegal fuel and pornographic discs.
Core triad members, drug traffickers, prostitutes and gamblers are among the 686 men and 505 women who were arrested.