Drunken revellers on Ruby Island had to be helped ashore by Wanaka emergency services.

Up to 500 people had to be rescued from an island in the middle of Lake Wanaka after a party got out of control and they became too drunk to get back to land.

Queenstown Lakes deputy mayor Calum MacLeod and the local harbourmaster heard about the event on Ruby Island, understood to have been organised on Facebook, and headed there on Thursday afternoon.

MacLeod was "less than impressed".

Supplied The party was believed to have been organised on Facebook and attended by up to 500 people.

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"It was the classic bad combination of alcohol and boating. Some people were too drunk to make it back on their own and if the harbourmaster's team and the coastguard hadn't been there, some of them would have come to grief."

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Craig Blake/QLDC "It was the classic bad combination of alcohol and boating," said Queensland deputy mayor Calum MacLeod.

The Coastguard, police and fire service were called to rescue some of the revellers.

One man was pulled from the water with his lifejacket draped over his arm because he had been incapable of putting it on, and he told his rescuers that he couldn't swim.

Others, who appeared to be heavily intoxicated, were turned back as they attempted to paddle to shore, and told to wait for a ride with the coastguard.

Marjorie Cook Ruby Island at the centre of Lake Wanaka.

MacLeod said organisers had encouraged people to paddle across to Ruby Island, generally in flimsy inflatable boats and with large amounts of alcohol, to drink on the beach.

The organisers had insisted that everyone who took part had to wear a lifejacket but no one was enforcing the rule when people began the return trip later in the afternoon and no one was keeping count of participants to make sure that everyone got back safely.

"Things would have gone horribly wrong if the wind had got up," he said.

The incident had all the elements for trouble on a large scale, he said.

"If you get pissed and fall down at a land based event you just end up looking like an idiot however if you get pissed and fall out of a small inflatable boat you could die."

Ruby Island was not a suitable location either and the organisers should have sought a resource consent.

"There is one long-drop toilet, they hadn't made any provision for food and water, or first aid. And they effectively shut out all the rest of the people who might have wanted to go over to the island yesterday."

When the scale of the event became apparent in the early afternoon, the local harbourmaster contacted the police, who in turn called in the Wanaka coastguard to help get everyone off the island and back to shore safely.

A fire had also been lit on the island in breach of the restricted fire season, and the harbourmaster had to ferry members of the volunteer fire brigade across to the island to make sure it was completely extinguished.