A turquoise-coloured substance floating on top of a river near Burnham-On-Sea sparked fears of a pollution incident this week.
But the Environment Agency insisted that the vibrantly-coloured material is harmless and poses no risk to people or the environment.
It was spotted about three miles south of Burnham in the River Parrett on several days – prompting fears of a chemical spillage.
However, Environment Agency spokeswoman Bridget Norris told Burnham-On-Sea.com: “One of our officers has been investigating and has found the blue substance is a harmless dye that has no adverse affects on the environment.”
“It’s a non-toxic, regulated substance that is a by-product used in the making of cleaning cloths,” she said.
She added that the Environment Agency would continue monitoring the area in coming weeks.
Members of Burnham’s hovercraft crew spotted the substance while out training in the river earlier this week.
Pilot Pete Emery said: “The substance was spotted on two separate days and seemed to be coming from a pipe leading from a nearby factory.”
“Given its bright colour and the quantity, we thought it was best to contact the Environment Agency.”