Essex Police said they were investigating the reason why persons coughed and struggled to breathe at a packed beach on the hottest late August bank holiday weekend on record.
Police, ambulance and fire service personnel were all called to the coast near Fourth Avenue in Frinton-on-Sea after receiving calls on Sunday.
It is currently unclear what caused the incident, however some in the area have speculated that the symptoms may have been caused by pollution from a fuel spill. But the Maritime and Coastguard Agency, which sent a counter surveillance pollution aircraft to the scene, said no evidence of this has been found.
Earlier this month a hazardous material left several people on Worthing seafront complaining of sore eyes and vomiting, and two requiring hospital treatment.
The coastguard said a passing cargo ship might have been the cause.
