A foam spillage travelling down the River Thames is being investigated by the Environment Agency.
The Environment Agency would not reveal the pollution's source
The fire-fighting foam has already killed fish along a three-kilometre stretch of Dudgrove Brook in Fairford, where the spillage was first reported.
Up to six feet of foam passed through Lechlade weir on Thursday and the spillage was also reported at Buscot, Radcot and Rushey locks.
The foam has also travelled down the River Colne, killing more fish.
Environment Agency officer Emma Bateman said: "We are keeping a close eye on the progress of the foam down the Thames.
An investigation has begun into the incident
"We have received reports that people have suffered from sore throats and itchy eyes if they are near it, and if members of the public experience these symptoms they should seek medical advice.
"Fisheries officers are also assessing the impact of the foam on local wildlife and we will continue to do so."
The Environment Agency would not say what the source of the pollution was.