Parts of the River Sence, which runs from Charnwood Forest and Coalville to Hinckley, were found by locals to have suddenly turned an unnatural shade of blue.
When other residents had saw it, many locals tried to guess what had caused it.
Many guessed the water was being treated to kill algae off and one person even questioned if the photos were real, asking if the images had been photoshopped.
But despite the river’s vibrant colour, a spokesperson for the Environment Agency said that it was harmless.
