GLENN Harcombe claims he was threatened with a knife and thrown into the ocean after an altercation at the Rockingham jetty.
Mr Harcombe lives on a yacht. He came into shore with his partner for some grocery shopping on Saturday.
Mr Harcombe said there were a lot of people fishing at the jetty and he asked one of them to pull up their line so he could moor his dingy.
Police said there was an exchange between Mr Harcombe and the man fishing. The man told Mr Harcombe he would gut him like a pig.
Police said the man had a 15cm fishing knife, which he pulled out of his pocket. They said the man grabbed Mr Harcombe around the throat and threw him into the water.
The incident happened at about 1pm and there were lots of people around.
Police are investigating and described the man fishing as about 35 to 40 years old, with olive skin, about 185 to 190cm and a stocky build.
He was wearing a high visibility orange hunting-style utility jacket.
Mr Harcombe said there was a lot of anti-social behaviour on the jetty.
He said people left their rubbish behind and the jetty smelt from people leaving behind fish guts and urinating.
“Hardly a good look for tourists,” he said.