The aquamarine lagoon edged with white sands is a key location in Pacific mythology, known as the reputed point of departure for a band of Polynesians who sailed to establish what became New Zealand.

Now lined with premier hotels, it is regarded as a sparkling blue jewel in Pacific tourism.

Toxicologist Mark Skinner, however, told a public meeting here that all was not sparkling beneath the surface, as streams feeding the lagoon were polluted well beyond standards accepted by the World Health Organisation (WHO).

The WHO sets the standard for human and animal waste, or faecal coliform, at 50 cells per millilitre of water.

In the Muri Lagoon, Skinner told the Cook Island News, "we are talking about thousands of cells when you only need 50 to be in the danger zone."

"The degradation of the lagoon is continuing and it needs to be addressed. There are a lot of toxins there."

Skinner said high levels of nitrogen and phosphorus, suspected by locals and confirmed in test samples, have helped create green algae blooms in the lagoon, adding that small drifts of dirt-coloured sediment in lagoon sands are a type of poisonous micro algae that may be unique to the Cook Islands.

The government has yet to react to the study but former prime minister Geoffrey Henry expressed alarm at the news his favourite swimming hole was becoming a toilet bowl.

"It is obvious something needs to be done," said the opposition leader.

TERRA.WIRE