The number of children swimming in Liverpool public pools has almost halved since free leisure passes were scrapped in August to save £300,000.
Council figures reveal that the number of nine to 17-year-old swimmers has dropped from 15,000 in 2009 to 8,000 this year during September and October.
Figures for older people, who also lost their free passes, increased over the same period from 12,600 to 14,350.
A council spokesman said older people may be tempted by less busy pools.
'Weight and obesity'
He said: "In common with other local authorities, we have regrettably had to reintroduce charges for swimming after the government scrapped the grant funding support for free access for under 17s and over 60s.
"We have tried to keep the cost of admission as low as possible, and at between £1.50 and £2 per session we believe it is extremely competitive. Under nines are still admitted free of charge.
"It may be that the over 60s are enjoying the extra space in some of the pools as fewer young people are now swimming," he said.
Wendy Simon, the council's cabinet member for culture and leisure said that research was being carried out to discover which pools were used the most by young people in order to assess whether free swimming could be reinstated at those centres.
She said: "The figures for weight and obesity are concerning us in Liverpool and if we can get young people into a pattern of regular exercise and good diet from an early age then that would be really good."