Richard Davies suffered breathing difficulties after going for a swim
Ten children and a man were taken to hospital with breathing problems after being overcome by chemicals at public swimming baths in Liverpool.
Richard Davies, 30, was given oxygen for six hours to help his breathing after paramedics arrived at Lifestyles Centre in Garston on Wednesday night.
Ten children, who had also been in the pool, were taken to Alder Hey Hospital.
Liverpool City Council said an inquiry had started and the Health and Safety Executive (HSE) had been informed.
Paramedics at the scene told the victims they believed too much bleach and another cleaning fluid had leaked into the swimming pool.
Mr Davies, from Aigburth, had swam 30 lengths before he experienced a burning sensation at the back of his throat and had trouble breathing.
He added: "It was pretty strong tasting and as I was swimming I heard people screaming 'get out, get out'.
The Health and Safety Executive (HSE) has launched an investigation
"It was total pandemonium, parents were looking for their kids, and the children were screaming and retching.
"I couldn't breathe properly and felt myself staggering around. It felt like the air was burning. One of the girls looked in a pretty bad way."
Ambulances arrived at the leisure centre, on Long Lane, just after 2100 GMT.
Mr Davies, had chest x-rays and blood tests and was kept overnight under observation.
"It was horrific," he added, "I went for a swim and ended up in an ambulance on oxygen. Exercise isn't supposed to be this bad for you."
The swimming baths have reopened following water tests on Thursday, a spokesman for Liverpool City Council said.