HE'S been working on the water for more than 30 years, but Ken Smith had never seen a box jellyfish float by his boat - until Wednesday.
The skipper of the Mikat was returning from a charter when he saw the marine killer float by, in the waters of the Gladstone marina.
Grabbing a bucket, he scooped it out - but after making calls to Queensland's department for marine parks and researchers, he doesn't know what to do with one of the world's most venomous creatures.
"No one wants it, but I don't want to put it back," he said.
"It's only a juvenile, but it's already big enough to kill 10 men.
"I've seen a lot and I've even been bitten by a shark, but these are the worst - most times, the victim's dead even before they're out of the water."
In 2009, a 10-year-old girl survived an attack in the Calliope River, and Captain Smith said Gladstone harbour was a breeding ground.
"People need to know they're (box jellies) out there," he said.