The main pool at a leisure centre has been closed for the day after a deep clean operation was launched following an incident.
Durham County Council has shut the large pool at Freeman's Quay in Durham city centre.
The authority has confirmed it is due to a "hygiene incident."
Mark Lee, its locality delivery manager, said: “Following a hygiene incident we have closed the main pool at Freeman’s Quay for a 32 hour deep clean process.
"Our customers rightly expect the highest standard of water and we follow national best practice guidance to ensure that is what we deliver.
"The small pool and the rest of the centre are operating as usual and we will have the large pool open again tomorrow morning.
"Unfortunately these things happen and we thank our customers for their understanding.”
A post on the council's Facebook page said: "We have had to close the large pool at Freeman's Quay in Durham all day today, so unfortunately all lessons and activities in the main pool are cancelled.
"We are ringing round people but if you can help us spread the word that would be great .
"The small pool is open as usual and we hope to have everything back to normal tomorrow.
"Apologies, it's unavoidable
"Please contact FQ for further info if you haven't been called."
Anyone who needs more information on the impact on services can call 03000 268 488.