The Environment Agency is looking into reports of a foam cloud that has settled in a Northampton lake.
Residents spotted the eight foot-high froth at Shelfleys Lake, in Ladybridge Park, Wootton, on Sunday and notified the authorities. The lake is fed by Wootton Brook.
No-one seems to know what substance has entered the water but some residents have speculated that it is washing up liquid, with the wind stirring up the lake and creating a giant bubble bath.
An Environment Agency spokeswoman said it was aware of the incident and was looking into the cause:
“We’re investigating the source of foam, likely from detergent, which appeared on Wootton Brook over the weekend.
"There is no more foam entering the water and what is there will be diluted as it works its way through the system.
The Environment Agency said it does not believe the substance poses a risk to fish, wildlife or the wider environment.
However it asked that if anyone still has concerns to report them to its 24-hour hotline by calling 0800 80 70 60.
Ian Delaney, who photographed the foam on Sunday, speculated that chemicals caused by decomposing leaves and the movement of the water may have caused the strange effect.
He said: "it was quite solid and, considering the strong flow of water and the wind, that's strange.
"I've lived nearby for more than 20 years and I've not seen anything like it."