Peter Thimio, 33, runs Big Pete's Swimming school and held classes across the Greater Toronto Area, including at some GoodLife Fitness Clubs.
Police say a 15-year-old female employee recently came forward with the allegations.
Police allege Thimio assaulted the underage girl over the course of a year from 2010 to 2011.
GoodLife management says they are severing ties with the instructor and will no longer let his company rent their facilities.
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