Investigations are continuing into how beachgoers were left struggling to breathe on a packed beach during the hottest late August bank holiday weekend on record.
Several families on the beach at Frinton, Essex, reported having trouble breathing on Sunday.
Police have advised people not to enter the sea on Monday.
The Maritime and Coastguard Agency said received reports of swimmers suffering from a possible respiratory irritant.
It said there was no evidence of any fuel spillage from vessels.
The ambulance and fire service attended the scene shortly after 14:00 BST on Sunday.
One mother described how one of her twin daughters was left “gasping” for breath.
Miriam Lansdell said: “My daughter started coughing. She said, ‘I don’t feel good. It hurts to breathe in’.
“My other daughter was gasping and couldn’t form words because she couldn’t breathe well enough.”