The tragedy happened at Hambleton Leisure Centre, Northallerton, at about 4.25pm yesterday.
The boy, who was local, was taken to the Friarage Hospital in the town, where efforts to revive him failed.
A North Yorkshire Police spokesman said: "Police inquiries to determine the full circumstances surrounding the death are ongoing."
A Hambleton Council spokesman said the pool would remain closed until further notice as a mark of respect.
A spokesman said: "This is a tragic accident and we send out condolences to the family of this young boy."
Councillor Peter Wilkinson, cabinet member for health, which incorporates leisure, said "It is a tragedy and our condolences go out to the family. Losing an eight-year-old like this must be horrendous."
Coun Wilkinson believed the boy drowned in the centre's 25m pool. According to the council's website, the baths have "fun features including flume, waterfall, waves and geysers".
Coun Wilkinson said lifeguards employed by the council work at the centre, which was busy during the schools' summer break.
He said: "I would say our safety record is excellent and we have never had any issues to my knowledge. I am newly-appointed to the cabinet (but) I believe we have never had a tragedy like this before, and I hope we never have another one."
The councillor did not know the dead child's identity and said North Yorkshire Police would wait 24 hours before releasing his name.