A wild dolphin in New Zealand is in trouble with authorities again.

Moko the dolphin became a tourist attraction on the North Island after he swam into a harbour and never left.

About six months ago his mood changed; he began getting a bit aggressive and started liking human ladies a little too much.

He was in trouble for refusing to let a female swimmer go back to shore because he had not finished playing with her. The exhausted woman thought she was going to drown.

Now Moko the dolphin is in hot water for terrorising some young female lifesavers and headbutting a couple of surfers.

Moko might be cute to look at, but he has a dark side and can get very moody.

The 200-kilogram wild dolphin lives in the water off Gisborne in the North Island.

Recently Moko has been trying to knock out the competition, going after men like local Dean Maraka who was knocked out of his kayak.

"He's starting to get a bit rough and he's getting annoying," he said.

Mr Maraka, who's a pretty tough-looking bloke, is now too afraid to go back into the water.

"He thinks he's just playing but he doesn't know what playing is," he said.

Grant Fussell, the president of the local surf club, has had to rescue six people terrorised by Moko in the past two weeks.

"The problem is we do have a lot of people going out and getting into trouble and they're not aware of his weight and his strength," he said.

"Some cases are not so serious - people wanting to get their surfboards back."

Jamie Quirk from New Zealand's conservation department says Moko has a mean streak.

"They've got 26 teeth in the bottom of their jaw. They can bite you, they can headbutt you," Mr Quirk said.

Mr Fussell says Moko could literally become a lady killer. He says Moko has lost his mojo with other dolphins and sees himself with a human partner.

"He relates more to humans," he said.

Although speculation at this stage, Mr Fussell says it is possible that Moko could try to mate with a human.

Marine scientist Mark Orams says people should be very wary of Moko as a "predator".

Moko's personal life is now under the spotlight.

The host of a nightly current affairs show asked Mark Orams the question many New Zealanders want an answer to - if they should venture back into the water?

But Mr Orams says the risk of him mating with a human is unlikely - it is more that he is trying to be dominant.

The local council has announced it is going to fine anyone who tries to swim with the dolphin, so it looks like being a long lonely summer for Moko.