A surly swan is terrorising a stretch of Nelson's Maitai River - chasing children, harassing a woman with a pram and having a hissy fit at a kayaker.
The male bird, known as Aragorn, this weekend attacked Dian Edmondson while she was kayaking.
The attack was so fierce she had to fend it off with a paddle.
She says she was told of other attacks on the same day.
When she first passed by the swan to say hello "he had his head down, tucked under his wings and I just thought he was being shy".
But later, as she passed a bridge, she heard a yell: "hey, he's going to get you" - and then the feathers began to fly.
"He actually physically got out of the water on top of my kayak, at the back. He had his wings stretched out ... attacking my kayak with his beak. All I know is my boat's shaking ... and I was screaming and carrying on."
After getting off the kayak, Aragorn charged Ms Edmondson in the same aggressive way.
"And he's coming really close to me, and he started hissing and trying to snap at me, so I got my paddle and pushed him away on his neck.
"Man, he was strong. It was really freaky because I was kind of at eye level with him.
"I kind of won that argument, and he decided to go away."
Ms Edmondson, of Atawhai near Nelson, was later told that the same day Aragorn was seen chasing children on the riverbank, and this week he chased a woman pushing a pram.
"It's not good. He might hurt someone one day. It's a warning for other people in our area here not to get to close to him.
"Anyway, it was quite a experience. So I don't think I'll be going up that river anymore until he's gone."
Swans can be aggressive in defence of their nests, and there have been reports of attacks on people and small watercraft that enter their territories.
Nelson Marlborough Fish and Game manager Neil Deans said the problem was that a swan's "regal" appearance made it seem harmless.
"People forget that there are domestic pets, and then there are wildlife. And you can't expect them to do what you would like."
The mute swan species is protected under wildlife legislation.