An Australian scientist has discovered that bacteria levels in the lagoon of the Cook Islands main island are twenty times higher than the limit set by the World Health Organisation.
Mark Skinner says his tests of streams flowing into Rarotonga's Muri Lagoon show massive amounts of poisons, possibly caused by farming by-product.
He says leaking sewerage systems from hotels lining the lagoon could also be a source.
Mr Skinner says even if the sources of the toxin were to be identified and cleaned tomorrow, it would be a decade before the water quality in the lagoon was acceptable.
"I would think a good ten years or longer before we can see some differences. I mean the thing about these microalgae is that it starts to take over the eco-system and affects the biodiversity of the rest of the lagoon as well."
Mr Skinner has called a meeting for tomorrow night to brief health and environment department officials and representatives of the tourism authority.