Tests have failed to reveal the cause of a mystery illness which saw beachgoers suffered breathing difficulties, vomiting and coughing.
About 150 people fell ill at the Essex resorts of Frinton-on-Sea, Clacton and Walton-on-the-Naze.
Fourteen people were treated at Colchester Hospital after the outbreak on 25 August.
Tendring District Council said water samples had not revealed any answers.
No-one ended up being seriously ill and Environment Agency tests on water samples taken from the sites have found nothing unusual.
Will Lodge, Tendring District Council communications manager, said: “We are pleased that the analysis revealed nothing untoward, and the absence of any further reports of similar problems since 25 August suggests whatever caused the incident has now passed.
“While it is frustrating we are not able to conclusively say what caused this, we are now assured whatever it was is not ongoing.”
The council said incidents such as this were not unheard of on the country’s coastline.
The Maritime and Coastguard Agency said there was no evidence of a fuel spillage from a vessel while Centre for Environment, Fisheries and Aquaculture Science said there were no algal blooms discovered in the water.
There have been other cases of people becoming ill on beaches during the summer.
On 11 August, Worthing seafront was evacuated. Investigators concluded hazardous material could have come from a nearby boat.
In August 2017, about 150 people attended hospital in Eastbourne reporting sore eyes and vomiting. An investigation suggested a gas cloud came from the Channel.