Blitz the Gap is a pan-Canadian initiative to guide citizen science with sampling ‘challenges’, bioblitzes and paid initiatives using iNaturalist. One summer of semi-guided sampling helped to gain 540 species newly recorded on iNaturalist Canada, almost 50,000 km2 of added spatial coverage, better representation of northern climates, and new evidence to help identify Key Biodiversity Areas. Bioblitzes and paid initiatives were particularly successful with participants collecting 3-5 times more observations than background rates. Citizen science initiatives are more and more critical in filling biodiversity knowledge gaps. As countries work towards global conservation targets for 2030 and 2050, citizen science should be one of the core pillars of any large-scale monitoring network, contributing unparalleled taxonomic depth and public engagement.