Two Canadian inventors of giant ice resurfacing machines that tame the Rideau Canal each winter into the world’s largest skating rink have lost the patent for their unique contraptions because email alerts warning of an unpaid patent fee were caught in a junk mail folder.

Known as Frosters, the machines crawl along the Rideau Canal Skateway at night, giving the nearly eight kilometres of outdoor ice that winds through the heart of Ottawa its smooth, hard surface.