A swimming coach said she had to turn away 100 disappointed youngsters after the pool where they have held lessons for 40 years closed unexpectedly.
Wimbledon Leisure Centre said they notified Merton Swordfish head coach Deborah Pitt of a mechanical fault at the Latimer Road pool two hours before lessons were due to start, but Mrs Pitt disputes this.
She said she waited for hours outside the venue turning families away having not been told of the closure for safety reasons on Monday, March 31.
The club has apologised to families who were left disappointed by the lack of lessons on that day. Mrs Pitt said: "There were some angry families.
"I stayed there until 8.40pm to make sure everyone knew.
"We will be fighting for a refund.
"It is £150 to hire the pools and it closed with no explanation."
A spokesman from GLL, the company which manages the centre in partnership with Merton Council, said the pool was closed the day before on Sunday, March 30 due to a mechanical fault that impaired the visibility of the water for lifeguards.
It is understood air was drawn into the circulation vent which caused an "excess of bubbles".
A spokesman said: "To ensure customer safety, the pool remained closed until Monday, only opening for a small swim class in a contained area of the pool.
"This followed a full risk assessment and public swimming was not available during this time."
The Merton Swordfish Swimming Club has been based at the centre for about 40 years.
Monday night lessons run from 6.30pm to 8.30pm for youngsters aged four to 19-years-old.
GLL said the fault has now been repaired and normal service resumed from Tuesday. The company apologised for any inconvenience this may have caused to the swimming club.