Holidaymakers have been told to keep away from beaches in northern France covered in seaweed after doctors gave warning that it could give off lethal fumes when it rots. A stretch of beach had to be closed after a horse rider lost consciousness as a result of the putrefying algae. His horse was killed. Local residents have also been treated in hospital. Green algae is collected from the beach at Saint-Efflam in Brittany The incident was in Brittany, where green seaweed is spreading across the region’s beaches as nitrates pollute the water supply as a result of intensive agriculture. Scientists...