People are being advised to not swim in St Aubin's Bay.
Infrastructure and Environment has issued the warning as a precaution.
It initially said technical issues mean the discharge from the sewage treatment works might not be working to its usual standard at the moment.
The Minister has taken to twitter to emphasise that no test results on seawater in the bay have come back yet.
Just to emphasise regarding this advisory notice that we will have more information tomorrow. So far, this is a precautionary warning following tests on water quality from the outfall from the STW. We have no test results for seawater in the bay yet. https://t.co/yuVVeaym8S— Jonathan Renouf (@JonathanRenouf) June 14, 2023
Later on Thursday (15 June), the government issued more details - saying the issue is down to 'environmental and biological issues'.
"Warm weather, little rainfall, a lower-than-normal load arriving at the STW and biological factors are all thought to have contributed to the reduced effluent quality."
Signs have been placed along the bay warning against going in the sea.
I&E Chief Officer Andy Scate said:
“We believe it’s a series of factors all happening at the same time, that have contributed to the discharge not being at the standard we’d like. Higher-than-normal ammonia levels are entering the Sewage Treatment Works, and there are low flows through the facility because of reduced surface water. Along with this, an overeffective initial stage means there’s a reduced concentration of organic matter that the bacteria require to function properly in the plant. This causes a reduced biological activity which affects the quality of the final discharge.”
The department is waiting for test results on the seawater to see if there is an increase in bacteria levels.
"We aren’t necessarily declaring that it’s dangerous to swim in the area, but we also cannot guarantee that there’s not an increased risk to swimming there. Until we can give that assurance, we ask that you please don’t swim in St Aubin’s Bay.” -Environment Minister, Deputy Jonathan Renouf.
Anyone who has been swimming there and now feels unwell should speak to their GP or call Environmental and Consumer Protection on 445 808.
Organisers of the Jersey Triathlon are waiting to hear if it will affect Sunday's planned event.
"We are in contact with officers from Government, who are monitoring this situation very closely and we are awaiting further updates as to whether this will affect the Accuro Jersey Triathlon swim discipline this Sunday.
As soon as we receive further information, we will update on any change of plans for this weekends event."