The Environment Agency has investigated a pollution incident after a stream in Warmley became the latest in Bristol to suddenly change colour.
Worried residents reported the unusual sight after the water in the Siston Brook abruptly turned blood red on the weekend of May 2-3.
One concerned woman said she saw the polluted water in nearby Kingswood, adding she walks her dogs in the area and that "they often drink from the stream".
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The Environment Agency has since confirmed that an investigation found that the shocking change of colour was caused by a dye entering the watercourse.
"We have received reports from concerned members of the public about a bright red discoloration of the Siston Brook near Fisher Road, Warmley, Bristol," a spokesman said.
"The pollutant was a type of dye that didn’t pose a serious risk to the environment."
He continued the dye came from a "particular location" but could not comment further, saying the agency was considering their options.
He said: "The pollutant did not have had a serious or lasting effect on water quality.
"Our investigation has now ended and we are considering our options."
The agency investigated a similar incident earlier this year after a stream in a Bristol park began regularly turning "milky white"
Residents were left baffled last November after the water in Mina Road Park in St Werburgh's abruptly changed colour.
The strange phenomenon took place once again in January, with the water returning to its usual colour less than an hour later.
Residents living nearby said this was a regular occurrence and were concerned about the impact of possible pollution, with the BBC reporting previously that a pet owner claimed his dog fell ill and started vomiting bile after drinking from the stream.
The Environment Agency confirmed at the time it was investigating the pollution but added the potential sources were "numerous" due to housing and industrial units nearby.
"The stream is culverted upstream taking input from a large area of housing and industrial units, meaning the potential sources are numerous," a spokesman said.
"We will continue to investigate but the short length of time it occurs for and the large area that drains to the stream make it difficult to trace without further information."
Similarly, the Environment Agency launched an investigation last year after part of a stream turned neon blue.
The agency tweeted a picture last August of the stream near Frome, one of the tributaries of the River Frome itself, which showed the striking colour of the water following a 'pollution incident'.
A spokesperson for the agency said at the time that tests were ongoing to investigate the source of the water's strange hue.
The EA has been contacted for an update on the investigation.
