A random audit conducted by Whangarei District Council found 10 out of 11 pools inspected were non-compliant.
The discovery has promoted a full review of all the swimming pools in the council database, amid concerns there are other pools that recieved approval in the past even though they didn't comply.
Whangarei has about 1500 private swimming pools.
Chief executive Rob Forlong said that early in March, council was contacted by an owner seeking code compliance for their property before it went on the market.
"During our inspection we discovered that the property's pool fence, approved several years ago, was not compliant and that it would be possible for youngsters to get through it and get into the pool area," Forlong said.