Year 4 pupil Liam Bush visited Salt Ayre with Trumacar Primary School last Monday morning.
His mum Tracey said when he returned home from school, she noticed his body had started to come up in a red rash and sores.
However, Lancaster City Council - who operate Salt Ayre - have said that while they are looking into the incident, there is nothing to suggest there were any adverse conditions in the pool when the school visited.
More than 700 swimmers used the pool on the day Trumacar visited, the council said.
Tracey said Liam's rash initially looked like sunburn, but quickly worsened.
"He had a rash on his shoulders and back when he got home," she said. "It looked like sunburn. I put some cream on and rang the doctors and then 111.
"It started turning into a bubble and moving to other parts of his skin, so his dad rushed him up to A&E. They said it was a chemical burn that they thought was from the chlorine in the pool."
Liam was given medicine at the hospital, but had to return the following day after the rash spread to his face and he was struggling to move his arms. His lips and tongue were also affected.
"It covered his whole body," Tracey said. "They said it would have turned to blisters if we hadn't got him there quickly.
"He was in pain and it was really upsetting for him."
It took until Friday before the rash had started to reduce on Liam's skin, and fortunately he had recovered by the weekend and was able to return to school this week.
However, Tracey said the whole incident has now left him scared to go in the pool again.
"He went back to school on Monday but he now never wants to go swimming again," she said.
Tracey said she was told other children had also been affected.
The family contacted both Salt Ayre and Lancaster City Council, who operate the pool, to express their concern.
A spokesman for Lancaster City Council, said: “The safety and wellbeing of visitors to Salt Ayre Leisure Centre will always be our first priority.
“We have been in contact with the family regarding their concerns but there is nothing to currently suggest there were any adverse conditions present in the pool at the time of the school’s visit.
“On the day in question more than 700 people attended swimming sessions at Salt Ayre and the only cases that have been reported come from this one school. No other schools, clubs or individuals have reported similar issues.
“We have, however, commenced a review of our procedures and will remain in contact with the family and will provide them with any updates should they become available.”
Trumacar did not wish to comment.