Erin Town enjoys a dip in the ocean and would often nip to the beach to cool off during the recent sunny weather.
But recently she fell sick and was rushed to hospital for emergency treatment and it emerged she had contracted cryptosporidiosis.
Erin's mother Paulina Town, 45, then discovered the beach where her daughter swam in Ilfracombe, Devon, had poor water quality - and that's where she contracted the illness.
Erin became unwell after swimming at Wildersmouth Beach, where swimming is not advised due to the poor water quality.
But Ms Town said she had no idea the water quality was so bad and wouldn't have let Erin swim there if she had known.
Ms Town said: "Erin and her friends have been swimming at Wildersmouth pretty much every day for the past two weeks since the weather has been good.
"Her temperature rocketed to about 40 degrees and she was having bad stomach cramps.
"Then she started vomiting and just couldn't keep anything down.
"Her tests showed this bug called cryptosporidium which they told me is common in water.
She added: "When I told the nurse that she had been swimming at Wildersmouth in Ilfracombe, she pulled a bit of a face and said several people had been ill after swimming there.
"She said she wouldn't even take her dog in the water there."
Erin stayed overnight at the hospital on Tuesday night and was discharged the following day.
But after becoming ill again, she was readmitted on Thursday for another night and had to go on a drip.
Ms Town said: "I was absolutely petrified, it was awful.
"We've lived in Ilfracombe for 12 years now and I never knew that you weren't supposed to swim at that beach. I had no idea the water was that bad.
"If we'd known I never would have let Erin go swimming there. The signs should be made bigger and more obvious.”
She also said that when she posted about the incident on Facebook, other people commented saying they didn’t realise you were not supposed to swim there.
"Erin certainly won't be going back in there again and I think it's important to let as many people as possible know about it,” Ms Town added.
"I would hate for anyone else to go through this, it has been petrifying."
Katy Nicholls, public protection manager for North Devon Council, said: “North Devon Council does not have any record of being notified about this incident by the child’s mother, nor have we received formal notification from any health body confirming a diagnosis of Cryptosporidium.
“We currently consider this to be an isolated incident and in light of Wildersmouth Beach being an undesignated bathing beach, we do not intend to take any further action.
“Our thoughts go out to the child affected by this condition and we wish her a speedy recovery.”
Join our new commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies