There are calls for regulation amid concerns over how they may affect fish and coral in the state’s tropical waters.
A device called the Jetlev can lift a person 30ft (9m) high by pumping water from a backpack through a hose connected to an unmanned boat.
Another contraption — the Flyboard — which looks like a small snowboard attached to a hose, can propel riders 45ft in the air. Promotional videos, racking up millions of views on YouTube, show riders shooting out of the ocean into the sky, then diving back in the water like dolphins.
The devices are starting to show up for rental in San Diego, Key West, Florida, and Cancun, Mexico.
But in the Aloha State, complaints from fishermen and others prompted the state Department of Land and Natural Resources to call a public meeting.
Randy Awo, the department’s top enforcement officer, expressed alarm about unsafe manoeuvres, such as riders dive-bombing into the water next to moving boats.
University of Hawaii coral scientist Bob Richmond told officials he was concerned about the noise the devices make, as fish avoid areas that are too loud. He is also worried fish and coral larvae could get pumped through some of the equipment the watercraft use and die.
Fisherman Carl Jellings said watercraft already scare fish away from Oahu’s bays, and worries these new machines will just add to the problem.
“More and more and more these bays are being run over, taken over by other activities. The marine life that depend on these places — they’re being displaced,” he said.
The state may find a way to accommodate the devices, perhaps in selected places, said William Aila, chair of the Board of Land and Natural Resources.
But he said studies are needed examining how such watersports may affect fish and coral.