Cheshire East Council has carried out an investigation after a group of teenagers were taken ill last month having spent the afternoon splashing about in the River Bollin, near Wilmslow Park South.
Around 36 hours after being exposed to the water some of the 14-year-olds started to get poorly, suffering from diarrhoea, vomiting and back pain.
The Environment Agency referred the case to Cheshire East Environmental Health Services who have been working with Public Health England.
A spokesman for Cheshire East Council, said: "The Council has conducted a thorough investigation into the incident of schoolchildren falling ill after swimming in the River Bollin in September.
"We have worked very closely with Public Health England on this and the findings suggest that the illness was caused by a viral infection resulting from swimming, in or exposure to, river water.
"The Council would like to remind people that, while river water is perfectly safe for wildlife, it may not be suitable for humans to bathe in.
"Cheshire East has written to all the parents of the schoolchildren affected by the incident and we can confirm that no further incidents of illness have been reported."
