Environment Agency officers were called in after water in a Grove brook turned bright green.
Investigators were called to Pill Ditch after residents noticed the water had changed colour yesterday.
Scientists said the substance was not toxic or dangerous to wildlife.
Agency spokesman Maria Goodall said it was trying to discover the source of the problem.
She said: "This substance will just naturally break down in the water. We know what it is, but we can't confirm where it's come from at this stage."
Mother-of-four Hazel Smith, 38, of Mayfield Avenue, Grove, said the stream changed colour in about an hour.
She added: "It was very green - the greenest green you have ever seen in your life. We were concerned about the wildlife and the effect on the water table."
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