A refurbished Whanganui East Pool is on track to be open by Christmas.
The complex had been undergoing a $300,000 refurbishment which included an excavation of the main pool.
Before work began on November 11 an x-ray of what was under the pool surface found an "anomaly".
Council's sport and recreation officer, Keith Smith, said when the area was excavated contractors found a tree trunk underneath "compromising" the area.
That was removed, the ground compacted and the concrete surface of the pool relaid.
A new sparge pipe – which keeps the pool topped up – had been laid along the centre of the pool and rusting pipes along the side of the pool have been replaced with stainless steel.
The pool surfaces have been repaired and repainted.
Mr Smith said the pool should open as planned on December 22.
"I can't speak highly enough of the contractors who are doing an absolutely brilliant job knowing that they are under the pump to get the job done."