110 people were evacuated from the building, after visitors reported nausea and eye and throat irritation.
46 people received treatment by ambulance staff at the scene before being discharged.
A man and a woman were taken to hospital for further checks as a precaution.
Stoke-on-Trent Police remain outside the water park this evening, alongside Staffordshire Fire and Rescue and West Midlands Ambulance Service.
Emergency services were called to Waterworld in Festival Park at around 1:55pm today.
Two ambulances, Hazardous Area Response Team (HART) paramedics, four paramedic officers, a BASICS emergency doctor and the Midlands Air Ambulance from Cosford with a doctor and critical care paramedic are in attendance.
One eye-witness said swimmers were made to stand outside as the air ambulance landed behind the Best Western Plus hotel.
Staffordshire Police were called at 2pm today by colleagues from the ambulance service to a report of guests feeling unwell at a waterpark in Etruria.
"The building has been evacuated as a precaution.
"A road closure has also been put in place on Festival Way to allow access for the emergency service response vehicles."
West Midlands Ambulance Service said: "Waterworld was evacuated after a number of people inside began displaying minor symptoms including watery eyes, a runny nose and nausea. A total of 110 people evacuated from the building who were displaying symptoms were rapidly triaged by the team of ambulance medics. Once triaged, 46 out of the 110 people received treatment by ambulance staff on scene before being discharged. A man and a woman were conveyed to hospital for further checks as a precaution.
“This was a well-managed tri-service response which saw the safe and speedy evacuation of a large number of people. Thankfully no one involved was in a serious condition."