Samples of water from the River Otter at Budleigh Salterton have tested positive for Norovirus.
East Devon District Council Environmental Health officers were alerted to the issue when a number of children, who had been playing in the river, became ill with severe vomiting. It is possible to contract Norovirus from person-to-person contact but in this case it is believed that the source is the river water.
It usually takes 24 to 48 hours for symptoms to appear, and these may last for 12 to 60 hours. Typical symptoms are vomiting, diarrhoea and stomach cramps. People affected may also experience high temperatures and tiredness. For healthy individuals the infection is likely to be short lived but can lead to dehydration.
Signs advising the public not to bathe or paddle in the river were put up on Friday, near the mouth of the River Otter at Lime Kiln.
An EDDC statement said "This has been a particularly difficult summer for maintaining good water quality and the rivers have been flooded several times. Flood waters take run-off from fields as well as excess water from the drainage system, and may take some time to clear."