Seagull poo may be to blame for poor Southsea pier water quality
Investigations are under way to find the cause of a rise in water pollution near a popular beach.
A water sample taken by Portsmouth City Council to the west of South Parade Pier on Southsea seafront revealed a drop in quality.
Southern Water warned the issue might be E. coli caused by seagulls roosting under the pier.
The Environment Agency said it was working to identify and remove the source of the pollution.
It could trigger advice from the agency for people not to swim in that stretch of water.
The investigation is also looking at other possible causes, such as leaks from small pipes, ongoing coastal defence works, contaminated groundwater and potential sewage releases by Southern Water.
But the council said there were no sewage outfalls in the area.
A Southern Water spokesman said it was testing the E. coli found in the water.
He added: "By looking at the samples, we can find out the type of animal source it comes from."
The council warned if the water is rated poor by the Environment Agency it would be forced to advise people not to go into the sea on that stretch of beach from next May.
The Environment Agency said it was working with the council and water company to investigate the reasons for the decline in bathing water quality.
"All agencies involved are working to identify, remove and reduce sources of pollution to ensure that the status of this bathing water improves," it said.
"The pollution sources appear to be localised and possibly coming from contaminated groundwater."
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