Police said emergency services worked to resuscitate the whitebaiter for more than 40 minutes, but he was pronounced dead at the scene.
A staff member from Lake Ferry Hotel, who did not wish to be named, said emergency services arrived at the scene about 2.30pm.
"He was whitebaiting and customers from the hotel spotted him ... scoop his net into the water, and he got swept out of the lake mouth and into the sea."
The hotel worker said staff rang emergency services straight away.
Eventually, a man jumped into the water at the lake mouth and swam out to the whitebaiter.
"He put on a life vest and swam out to the man - but by the time he got to him he was unconscious."
She said emergency services then tried to resuscitate the man.
Lake Ferry Hotel is on the shores of Lake Onoke. The lake mouth is a popular spot for locals to fish, she said.
"It doesn't happen very often. It's obviously something that is a danger, but it is not a common occurrence."
She said the man had been fishing at the spot for a while.