A pupil needed dialysis and humor transfusions aft swimming successful the oversea pursuing a sewage spill, her mum said.
After getting E. coli, Caitlin Edwards developed haemolytic uraemic syndrome (HUS) which damaged her kidneys.
Jayne Etherington said her 22-year-old daughter's "horrendous" five-month ordeal began aft she swam successful the oversea conscionable disconnected westbound Wales successful past summer.
"She'd gone from a happy, healthy, vibrant 22-year-old to looking similar she was going to die," mum Jayne said.
Caitlin had gone for a dip astatine the formation astatine Amroth successful Pembrokeshire, a fewer miles eastbound of Tenby, and did not cognize astir the untreated sewage spill astatine Wiseman's Bridge, conscionable down the coast, connected 24 August, 2022.
At the clip it was reported tempest sewage was discharged astatine 4 beaches, including Wiseman's Bridge and Saundersfoot, with Welsh Water saying the spill came from combined tempest overflows (CSOs).
But Welsh Water said the Wiseman's Bridge spill was from a backstage root and thing to bash with them.
"We were allowed to judge it was a CSO spill," said Jayne.
"No-one said, 'This is thing much serious'."
After leaving her location successful Pembrokeshire and staying successful London with her boyfriend, Caitlin started having tummy cramps and diarrhoea.
Her mum said she wasn't called until she was successful the resuscitation department.
Jayne said the household "didn't cognize she wasn't" going to die, adding: "It was horrendous."
Jayne said Public Health Wales (PHW) investigated what Caitlin had eaten and recovered the likeliest origin was untreated sewage arsenic harmful bacteria had entered her intestine.
Caitlin has present made a afloat recovery, completed her English and Spanish grade and is present moving successful Canada moving children's camps.
PHW said it could not remark connected idiosyncratic cases and Welsh Water said the spill was not down to them.
Pembrokeshire assembly said it had placed informing signs connected the formation "acting connected accusation received regarding a contamination incidental from Natural Resources Wales".
NRW said its probe into the Wiseman's Bridge contamination concluded "the effluent discharge was owed to a backstage discharge constituent failure".
"The owners of the backstage discharge constituent acted instantly to resoluteness the contented arsenic soon arsenic possible," said Nicola Mills of NRW.
"Our officers person visited the country since and determination person been nary further concerns witnessed oregon reported.
"Around the aforesaid clip determination was besides an ongoing CSO discharge truthful it was not imaginable to pinpoint sole work for the nonaccomplishment of bathing h2o sampling astatine Wiseman's Bridge."
The organisation said Amroth and Wiseman's Bridge were sampled connected the aforesaid day.
"Results from those tests showed a nonaccomplishment successful h2o prime astatine Wiseman's Bridge but not astatine Amroth," Ms Mills said. "Every discharge outlet has its ain licence limits."