Fire engines were called to Corby and East Midlands International Pool last night following a chemical spill.
The emergency services responded to call at about 5.30pm after sodium hypochlorite and sulphuric acid were spilled in the building’s plant room.
When mixed, there is a danger the chemicals can release harmful fumes.
The building in George Street was then shut at about 7pm on the advice of the fire service, and as a precaution.
Nobody was hurt and there was no immediate danger to the public.
The spillage was contained and cleared up overnight by a specialist company.
The swimming pool reopened at 6.30am today and is now running its usual service.
Leader of Corby Borough Council Cllr Tom Beattie said: “We would like to apologise for the inconvenience caused to our customers in yesterday evening’s incident although we are pleased that the safety and wellbeing of everyone was kept and no one was harmed throughout.
“We would like to say a huge thank you to members of the public and staff for cooperating fully and to the emergency services who helped us make a swift return to business as usual. An investigation is already underway and we will learn the lessons that need to be learnt from this unfortunate incident.”