Auckland Council says safety concerns about keeping an eye on 900 children a day - double the normal attendance - have forced it to restrict access to its big Henderson leisure centre.
The council's kids-for-free entry policy is being blamed for overcrowding at West Wave, the most popular of the council's 22 pools.
Last night, Mace Ward, who is council manager of parks, sport and recreation, estimated a 30 per cent to 50 per cent increase in young casual visitors at the West Auckland complex.
"With both Easter and the school holidays falling in April, this increase is unlikely to be the regular monthly pattern," said Mr Ward.
Attendance figures for the other 21 pools across the region were still being collated.
Mr Ward said restriction meant no new swimmers would be admitted until numbers returned to the figure in operations guidelines.
The policy has upset other pool users, many of whom have contacted the Herald.
One reader commented: "My husband tried to take our two daughters yesterday and they were refused entry.
"He is a monthly fee-paying gym member - the use of the pool is included in his membership and he was not able to go in."
Mr Ward said restriction included access for members specifically coming in to use the leisure pool.
"First and foremost, restricted swim sessions are put in place to ensure the safety of our swimmers and exceptions cannot be made for members."
Members had access to the hydrotherapy pool, the main 50m dive pool, recreation centre and gym. "People generally do not have to wait more than 45 to 60 minutes when a restricted session has been put in place."
Restrictions had also been put in place when required at Glenfield Pool and Leisure Centre and the Tepid Baths. Some readers said they would prefer returning to user-pays so they could guarantee their swimming.
Mr Ward said the change had been well received by the public. "This week is the last of the school holidays and we expect demand to settle down somewhat once they are over."
Reader Jason Horn said: "Plenty of times I have had to tell my kids that we can't go to the pools because we can't afford them. Keep them free. Build more pools, they are obviously needed."
Council officers had expected the policy would bring holiday peaks and extra staff, including life guards, customer services and casual staff had been rostered on or were on call.
Before the change last month, Auckland Council pools charged children $4.60 at West Wave, $4.20 at North Shore Leisure and $4 at Stanmore Bay.
Manukau pools were free, while the Papakura charge was $1.10 for under-17s. Independently run pools charge children.
The casual swim charge at Olympic Pool in Newmarket is $5 and Mt Albert Aquatic Centre charges $5.90. Spokesmen for both said they had not noticed a drop in under 15-year-olds since the free-entry scheme elsewhere began.