British holidaymakers in northern France have been warned to be vigilant against an influx of toxic seaweed landing on the beaches in Brittany.
The warning comes as 28 wild boars were found dead on a Morieux river estuary beach, all thought to have been killed by toxic gas released by the seaweed as it rots.
Beaches in the area are popular with thousands of British tourists popping across the Channel for summer holidays.
The warning was issued by Brittany's Cote d'Armor regional government which said the potentially deadly seaweed was 'above a health alert level, but below severe danger level'.
Seaweed – which is a form of algae - is normally found on most northern French beaches. However, it releases hydrogen sulphide when it comes into contact with nitrogen waste flowing to the sea from intensive pig farms.
The seaweed has caused problems before. Two years ago, a council worker on a seaweed clearing team was poisoned by gas and taken to hospital in a coma, and a horse-rider in 2009 passed out while its horse died after inhaling gas.
Brittany marine biologist Alain Menesguen told the Daily Mail: 'This is a very toxic gas, which smells like rotten eggs. It attacks the respiratory system and can kill a man or an animal in minutes.
'It is likely to be a feature of any area where intensive farming methods are employed.'
Morieux mayor Jean-Pierre Briens said: 'We are very worried for the health of visitors to beaches around here.
'How could we be anything other than worried when animals are being found dead?'
The French government has been under pressure to control how intensive animal farms despise of waste. But, apart from employing teams of workers to remove the seaweed when it arrives, nothing else has been done.
Environmentalist Jean-Frangois Piquot predicted two years ago that government's clearing was not enough and the toxic algae would spread.
He said: 'There are about five beaches that are unusable in Brittany. The problem is getting worse.
'There is no doubt that farming is to blame. Brittany has 5 per cent of French agricultural land but 60 per cent of the pigs, 45 per cent of the poultry and 30 per cent of the dairy farms.'
'As our rivers are not long, the pollution does not have time to clear before the water reaches the sea. It enters a closed bay and the sunlight produces the seaweed.'
If you're going to brave it, definitely leave the dog at home...
Seaweed? It doesn't bother the Chinese!