The Clareview Recreation Centre was briefly closed to the public on Thursday night.
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A spokesperson for the city initially said a pellet shattered a outside window in the northwest part of the Edmonton Public Library branch located in the rec centre around 8:30 p.m.
Officials are now trying to determine if the object was a pellet.
The Edmonton Police Service was contacted and the building was put into lockdown as a precaution.
No damage was reported other than the broken window and police cleared the facility to reopen around 9 p.m.
CTV News Edmonton has reached out to the Edmonton Police Service for more information.
