A chemical cloud which forced coastline evacuations across East Sussex on Sunday is "very unlikely" to have floated over from northern France, authorities said.
Some 150 people required treatment for stinging eyes, sore throats and vomiting, but the effects of the unknown substance were "mostly minor", Sussex police said.
Despite the incident, thousands are expected to flock to beaches along the coastline on Bank Holiday Monday as temperatures reach up to 25C (75F).
In the past, chemicals have drifted across from European industrial units, but weather models indicate this was not the case on Sunday, according to the Met Office.
Forecaster Jay Merrell suggested a vessel in the English Channel may have been responsible for the noxious haze, but stressed nothing conclusive had been proven and that inquiries continue.
Bob Jefferey, of the Royal National Lifeboat Institution (RNLI) Eastbourne division, said it would be business as usual.
He said: "Whatever it was, it smelled like burnt plastic. It hung about and didn't move yesterday because there was no wind. The cloud seems to have dispersed today though.
"The hospital has downgraded the threat to pretty much non-existent now."
Mr Jefferey added that five people had to be rescued from rapidly rising tides yesterday, and urged beach-goers to watch sea levels.
People along the shoreline from Eastbourne to Birling Gap, near Beachy Head, were advised to close windows and doors on Sunday, but have been told it is now safe to open them.