Waterlogged doors and faulty locking mechanisms have been blamed for the incidents and the Central Otago District Council is still looking for a solution.
The Alexandra Volunteer Fire Brigade was called out to remove the door, as it was for the two previous incidents, in March this year and August last year.
Senior Station Officer Glen Gray said a mother and her two young children were in the changing room. The brigade arrived shortly after 12.30pm and took about five minutes to free the trio, who did not appear to be upset.
Council parks and recreation manager Mat Begg said in yesterday's incident the lock had jammed, despite regular maintenance done in the hope such a situation could be avoided.
It was taking so long to find a solution ''because of the way the doors are made up''.
They needed doors that would not absorb water and had locking mechanisms that would not stick.
''It's frustrating for whoever happens to be there.''
Pool staff had limited tools and were unable to get the door open themselves.
''It seems to lock in a pretty permanent state.''
Both family changing rooms at the facility have sliding doors and have trapped people.
In the August 2012 incident, a family of four were trapped for 20 minutes and in March, a woman and two toddlers were trapped for about 10 minutes.
