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Niagara IceDogs is the team Robertson played for before joining the NHL. The IceDogs are a major junior ice hockey team based in St. Catharines, Ontario, Canada. They are members of the Ontario Hockey League (OHL). Robertson played for the IceDogs for four seasons, from 2015 to 2019. He was a key player for the team, and helped them win the OHL championship in 2018.