An emergency plan at Letterkenny General Hospital has been stood down, after an earlier incident at a leisure centre.
Several ambulances attended the scene at Aura Leisure Centre in Letterkenny on Saturday morning.
It is believed several children fell ill while swimming in the pool.
Doctors and nurses attended the scene to assist the emergency services.
Five people have been taken to hospital for observation as a precaution.
No staff were affected.
Letterkenny Sinn Féin Councillor Gerry McMonagle was at the scene.
"There was about a dozen ambulances and fire tenders and the Gardaí.
"From asking and inquiring as to what happened, I was told there had been some sort of allergic reaction in the pool for the children - who were quickly evacuated by the Aura staff to a safe place and emergency services contacted.
Up to 6 children have been taken to hospital for treatment to a reaction they had to chlorine in the water at the swimming pool at the Aura Leisure centre. Most others have been sent home. #Letterkenny pic.twitter.com/3wHpKd4OtW
— Greg Hughes (@GregHughes2) April 20, 2019
"A number of children have become sick while they were swimming, and it seems there was some sort of reaction in the pool area."
"Those that needed further attention were sent to the hospital.
"Most of the children have been seen and released back to their parents and are now home."
"I haven't heard that any of the children are seriously hurt, and I hope that they're not.
"They've been taken to hospital for precautionary measures.
"I just hope that all the children make a full recovery from this incident".
The company - which has facilities in Dublin, Dundalk, Leitrim, Navan and Cork - said 'no comment' when contacted by Newstalk.
Main image: Aura Leisure Centre in Letterkenny | Image: ©2019 Aura Leisure