A marine algae which produces toxins and depletes oxygen levels in water is being blamed for killing thousands of fish in Cornwall.
Thousands of fish have died and washed up on beaches in Cornwall.
An algal bloom, known as Red Tide, is said to be responsible for killing the fish in St Austell Bay.
The algae produces toxins which are lethal to fish and shellfish and it also depletes oxygen levels which makes it difficult for marine life to breath.
Cornwall Council said it can also cause skin irritations and harm pets and advised people to avoid entering water where the algae or any foam is present.
Rob Preston, chairman of the Mevagissey Fishermen's Association, said the marine life in Charlestown and Porthpean, such as sand eels, Dover sole and weaver fish, had been particularly badly affected.
Mr Preston, who recalled a similar bloom devastating shellfish and crustacean stocks back in the 1970s, said fishermen were especially concerned about the effect the algae could have on stocks of Dover sole as it was already under threat in the area.
According to the Environment Agency, the algae is called "Red Tide" because it can bloom in huge quantities and turn the sea reddish-brown.
Peter Long, an analyst with the agency, said: "Marine algal blooms are a natural phenomena. A Red Tide is one of many such types which can appear in the oceans and seas at this time of year.
The toxin can become concentrated in the flesh of shellfish grown in contaminated waters
"Under certain conditions, such as warm, sunny weather it can form huge blooms, which can be miles across.
"These blooms can last for some time, but will eventually disperse naturally."
A spokesperson for Cornwall Council added: "In public health terms this algae is of interest because the toxin can become concentrated in the flesh of shellfish grown in contaminated waters.
"Samples of shellfish have been taken for analysis from a variety of sources, but the commercial mussel beds in St Austell Bay are not a hazard because they are not being harvested at the moment."
No beaches have been closed but the council said that anyone who comes into contact with the algae in any form should wash the exposed skin with clean water.
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