Chloe Waddell of Timperley, near Manchester, was found unconscious in her bed by her parents on Sunday morning, according to a report in the Manchester Evening News. They phoned 999 immediately and tried to resuscitate her, but she died before making it to hospital.
Chloe had been tipped to be part of Great Britain's swimming squad for the 2016 Olympics in Rio de Janeiro, having won the regional 800m freestyle title and competed in the Olympic trials last year.
She had been at a party on Saturday night after being presented with an Outstanding Achievement award in recognition of her success. Her parents collected her and took her home afterwards and she went to bed as normal.
"We are devastated," said Chloe's mother.
"Chloe was exceptionally outgoing, extremely popular and had a wonderful smile – she was always smiling at all times and she had a kind word for everybody at all times.
"There was never a dark day for Chloe, everywhere she went she had lots of friends. She was charming and polite, accepting and encouraging.
"We are devastated but we have got support from friends and family and that's doing a lot to help."
Chloe, who turned 16 in December, was used to a tough routine of rising at 4.30am every day to train towards her Olympic dream.
“She worked incredibly hard. She loved swimming, she was very focused on it and she wanted to go as far as she could," Mrs Waddell added.
"She was also bright academically, everything she did she gave 100 per cent. We are very proud of her.
"She gave up going on holiday with her friend to compete, she was so committed, so dedicated, she worked everything around her swimming."
Chloe had made the jump from Altrincham Swimming Club to become part of the British Swimming national squad, and had competed over 200m, 400m, 800m and in open water events at a national level during her competitive career.
Her coach, James Stannard, was one of many who have paid tribute to her, saying he was "deeply saddened and chocked".
"This news has rocked us," he added. "Chloe was so talented. She had qualified for the Olympic trials last year and this year she hoped to compete in the European Junior Championships," he said.
"She was so talented, but also in terms of school. She was someone who got straight A*s and she could have picked and chosen what she wanted to do with the next stage of her life."
Her headmistress at Altrincham Grammar School, Mary Speakman, echoed those sentiments.
"Everyone at Altrincham Grammar School for girls is shocked and deeply saddened by the terrible news about Chloe. She was a truly gifted student, who was a valued and highly regarded member of our school community," she said.
"She was an exceptionally talented swimmer, who had real prospects of a place on team GB for the Olympics in Brazil. She will be sorely missed by all of us and our thoughts are with her family at this difficult time."
Mark Rose, head coach of the City of Manchester Aquatics team, had coached Chloe as part of the Manchester Beacon Programme and he paid tribute to the young swimmer.
"Chloe swam at the Manchester Beacon and was a hard working, self motivated individual who always walked in with a smile on her face," he said.
"Her positive frame of mind at all times is a credit to her family, her coach, James and her team at Trafford. She will be sorely missed and all of us here at Manchester have her family and her team mates are in our thoughts."