Some of the best scientific minds in the world will this week focus on exploring any potential link between harmful algal blooms and fish farms.
The issue has been put on the agenda of an international algal bloom conference in Paris by senior scientist Lincoln MacKenzie, from Nelson research organisation Cawthron, who described it as a high priority.
His call comes as a toxic algal bloom has frozen the shellfish industry in Queen Charlotte Sound and in Tory Channel, where New Zealand King Salmon operates its Clay Point and Te Pangu Bay fish farms.
The scientists attending the Paris conference are part of the Geohab programme supported by the United Nations Educational, Scientific and Cultural Organisation (Unesco).
On March 23, the Nelson Marlborough District Health Board warned against eating kina, mussels, pipi, tuatua, oysters and cockles harvested from Queen Charlotte Sound and Tory Channel.
Mussel companies voluntarily stopped harvesting in these areas from March 11.
The blooms have no effect on fish, including farmed salmon.
The Alexandrium catenella algae causing the problem was first found at the head of Opua Bay two or three years ago. However, Mr MacKenzie confirmed cysts had been present in sediment on the sea floor for at least 10 years and possibly a lot longer.
Opponents of New Zealand King Salmon's plans to build new fish farms in the Marlborough Sounds argued at an EPA hearing in Blenheim last year that waste from fish farms could increase the frequency and extent of algal blooms.
However, Mr MacKenzie said nothing he had seen suggested a connection between salmon farms and the the algal bloom in Tory Channel. The major source of nutrition for algae was natural oceanic nitrogen.
He went on to say nitrogen levels in the sea were similar from year to year but this toxic bloom was new.People tended to link harmful blooms and fish farming but in most cases he knew of, good evidence did not exist, Mr MacKenzie said.
Cawthron was asking for scientists around the world to work together on the issue because a better understanding of fish farm impacts on water quality and biology would help minimise effects on the environment.