Bathing water restrictions in Worthing and Lancing caused by dredging at the Rampion Wind Farm site have been extended.
The works began on Wednesday and were due to take three days, but Adur and Worthing councils have confirmed the works will take up to a week.
During the time when the dredging is being carried out water quality at Lancing Beach Green and Worthing may be affected.
A spokesperson for Adur and Worthing councils said: “This activity was scheduled to last for 3 days but has been extended to 7 days; until 6th September.
“This could be delayed further and a second Abnormal Situation may be declared shortly after this has finished.”
When the works were first announced, the councils spokesperson said:
“The Environment Agency will be checking the progress of these works to ensure that the impact to the bathing water is minimal. Routine sampling is suspended during the course of this incident.
Members of the public with any concerns about water quality should contact the Environment Agency on 0800 80 70 60.