Children raised almost £2,000 for Comic Relief by swimming lengths equivalent to the distance between St Albans and central London.
Members of City of St Albans Swimming Club swam 1,682 lengths of the pool at St Albans High School for Girls on Thursday evening.
The group of 20 boys and girls, ages between seven and nine, raised £1,900 with their hour-long challenge.
Coach Richard Lees said: "All the coaches in the club agree the kids did a fantastic job, but it’s their parents who have amazed us.
"Their support for both the swimmers and the charity has made the difference.
"It has been a whole club effort."