People have been warned to stay away from an Oxfordshire stream after heavy rainfall led to sewage discharges from a treatment works.
Witney Town Council said environmental officers were sent to Colwell Brook after reports of issues at the weekend.
The council said the officers found sewage fungus visible from Colwell Brook into Queen Emma's Dyke.
Thames Water said some wastewater was allowed to overflow to prevent flooding to homes.
A spokesman for the firm added: "Of course this is undesirable, but we only do it when there is literally no alternative.
"It is the way the system is designed to operate and is permitted by the Environment Agency under these circumstances."
Notices have been put up in the area telling people to stay away from the water and to keep their dogs on leads.
It comes after a similar problem was reported at the site in November, the town council said.
In 2016, the Environment Agency said 1,700 fish were killed in a 2km stretch of Colwell Brook and Queen Emma's Dyke after a suspected chemical leak.
At the time, Thames Water said "high ammonia levels" were found in the water which it believed was due to discharges from its nearby treatment works.