Toilet water leaking from the cafe and changing room plumbing means the Ladies' Pool at La Vallette is closed until further notice.
Swimmers can't use the pool for the time being, amid concerns about foul water pollution.
The States says a routine water quality test last Monday (24 August) gave a 'poor' result but that a second test, taken two days later, showed the seawater in the Ladies Pool passed the 'good' quality benchmark.
Tobin Cook, who heads up Environmental Health and Pollution Regulation, said that yesterday (2 September) a red dye was put in the cafe and changing room plumbing and this showed there was a foul water leak.
Given this, the Ladies' Pool has been closed until the problem is fixed.
There is no issue with the water in Havelet Bay and so the Horseshoe and Gents' Pools are open.
Mr Cook says they will update swimmers when they know more:
"We know this will come as a disappointment to regular users of the Ladies’ Pool, but we hope that islanders can appreciate that it is in everyone’s best interests to close the pool while we investigate this further."
Vive La Vallette, which runs the facility, says it is co-operating fully with Environmental Health and is working to find a sustainable solution to the drainage problem. The cafe is open but for takeaways only.

Alderney vicar delivers life saving CPR
App launching to tackle loneliness in Guernsey
Guernsey football star Maya Le Tissier scores for England
New Guernsey form aims to identify dangerous road spots
GSPCA condemns dangerous cow-taunting video and urges respect for livestock
Crew sickness leads to Alderney flight cancellations
Pop-ups to highlight homelessness in Guernsey
Guernsey pub landlord welcomes tap relief proposal