Sienna Ahir, of Heath Park School, completed the challenge of swimming 2.5km through the Swimathon Foundation, in order to raise funds for Cancer Research UK and Marie Curie.
The 14-year-old has been participating in the sport since the age of six, and one day dreams of swimming the length of the English Channel.
Sienna's dad, Manjinder, said he is proud of his daughter who he has described as his "inspiration".
He continued: "I'm really proud that she's taken it into her own hands and said 'actually I want to make a difference' – the whole family is immensely proud of her.
"She was so focused, she was like a little dynamo, I bought her some swimming earphones so she had her Ed Sheeran music on in the background and she stormed to the finish with a big smile on her face.
"She's really passionate about it, she said she just wants to make a difference and help people, and the best way she can do it is to take part in these charity events.
"She enjoys going swimming on a leisurely basis, she's trained with me and set herself little targets. She wants to increase it, this year is 2.5km, next year will be a 5km challenge – I know she wants to end up doing 400 lengths."
In order to train for the challenge which she completed on May 14, Sienna went swimming around two times a week, setting herself target times to complete the swim by.
The schoolgirl has raised almost £400 so far, having more than doubled her initial target of £150.
To support Sienna in her fundraising effort, visit justgiving.com/fundraising/siennaahir