Cockle picking has been banned along the coast between the River Etel and Penthièvre in Morbihan.
Members of the public have been urged not to eat cockles or other shellfish from the area.
The department's prefect ordered the ban after it was discovered shellfish have been contaminated with naturally-occurring lipophilic toxins, caused by a bloom in algae due to favourable weather conditions. Eating contaminated products can lead to sickness and diarrhoea.
The ban - which takes in professional and recreational cockle fishing and picking and came into effect on Thursday, September 7 - will be in force until 'a satisfactory health situation is restored' the préfecture said in a statement.
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