The Rarotonga community has launched urgent action after the government declared the Muri Lagoon, a big tourism drawcard, a national disaster.
A large number of commercial properties don't have compliant sewage systems and that's contributed to a rapid growth of algae.
"Our infrastructure to deal with nutrients with sewage getting into our lagoons have never been addressed and therefore after 40 years or so we have got this national crisis," says Philip Nicholas, a traditional leader.
The problem is runoff from the rapid growth of tourist accommodation along the foreshore, many which don't have compliant septic tanks.
Combined with cases of raw agricultural sewage flowing into streams, unnatural levels of nutrients are now feeding the spreading algae.
"We monitor the public health the levels of bacteria in that lagoon very closely so it is safe for swimming but if you were to look at the ecological health the coral reef, for example, it's suffering a lot," says Ben Ponia, from the Ministry of Marine Resources.
The local community including residents and tourist operators have formed an action group.
"We all want it to come back to what it was twenty years ago, it can be done," says village leader Keta Williams.
The group has ordered environmental reports on ways to increase the flow of water in the lagoon.
Cyclones over the years have caused coral and rocks to clog up what once were numerous passages.
Up to 80 percent of accommodation managers have been given an April deadline to get their septic systems compliant.
"Without tourism the economy will go down. The golden egg is cracked, the government must get into action," says Mr Nicholas.
Meanwhile it's business as usual on Muri Beach where holidaymakers are assured they won't suffer ill affects from being there.