The closure of Marshall Street baths in London's West End forced pupils at three local primary schools to travel up to 30 minutes for their swimming lessons.
The Sicilian green marble pools, which were emptied in 1997, are among 15 baths in the capital listed on the London Pools Campaign's website as closed in recent years. A further nine are at risk.
Sue Hudson, spokesperson for the campaign, said: "This is an example of a perfectly usable pool being closed down because councils are watching the bottom line. It means 20 or 30 minutes less swimming time for pupils."
Hackney, one of the three Olympic boroughs for London 2012, currently has only one swimming pool after the council closed community pools in order to plough more than pound;45 million into its flagship Clissold leisure centre.
The centre ran three times over budget, and opened 18 months late - but shut down again after 18 months because of design flaws.
Campaigners say Hackney is an extreme example of a problem which affects the whole of London. They estimate there are only two pools for every 60,000 people in London. Ms Hudson said: "A pool a year closes in London.
It's all very well saying there's a pool within two miles but in the inner city, for children, that's often incredibly difficult to get to.
"Learning to swim is an incredibly important life skill, without it children are not only at risk of accidents but are prevented from holiday activities."
It is not all bad news, however. Campaigners have helped to save three London pools, including Brockwell and Charlton lidos.
And nine years after it closed, campaigners have won a small victory with developers of the Marshall Street site, being asked to submit plans to renovate the main pool.
Ms Hudson said: "There's still a long way to go but I'm pleased that the council seems to be taking a sensible approach at last. Now we have to hope others will follow suit."
A spokesman for Hackney council said: "While swimming facilities in Hackney have been reduced in recent years, we are pleased to say that they are on the increase and will be almost unrecognisable a year from now."