The group said scientific studies strongly suggest a contributing factor to the tides is high levels of nitrogen from the fish farming industry. High levels of nitrogen foment the growth of algae, both toxic and nontoxic.

"There is evidence that strongly suggests a relationship between aquiculture and harmful algae," Alejandro Buschmann, a marine biologist who did a study for Oceana, told reporters at a news conference.

Oceana said the government should not give any more permits out for new salmon farms and should study ways to make the industry safer for the environment, including the nitrogen problem as well as stronger monitoring of the industry for use of internationally banned anti-fungals.

"This needs to be taken into account by the government and taken on as a problem for the country," said Oceana's director in Chile, Marcel Claude.

A spokeswoman for the Salmonchile association that represents the industry said the group was working on a statement about the Oceana assertions, which she said were false.

The Gulf of Ancud and fjords and inland channels in southern Chile have seen a huge growth in salmon farming in recent years.

Salmon is an imported species to Chile, but the country is now the second biggest salmon producer in the world, just behind Norway.

The salmon are concentrated in huge cages in the sea and fed pellets made from other fish. Buschmann said protein from the unconsumed food and the salmon's fecal matter release a huge amount of nitrogen into the water.

Chile exported 350,000 tonnes of farmed salmon and trout last year, more than triple the volume 10 years ago.