Citizen or community science (CS) projects in the marine environment rarely consider carbon footprint and sustainability. In this case study, we assessed the effectiveness of ten CS methods used by tourists in the Great Barrier Reef Marine Park (GBRMP) and Coral Sea Marine Park (CSMP) who participated in the 2023 Citizen Science of the Great Barrier Reef expedition and the carbon footprint associated with these field methods. We also assessed the baseline coral reef knowledge of the tourists, observations of marine species, and the communication of our results to the public. Specifically, the tourists utilised up to ten methods: iNaturalist, CoralWatch, Great Barrier Reef Census, Eye on the Reef (EoR), environmental DNA (eDNA) testing kits, photogrammetry, social surveys, and Red Map, as well as marine debris and marine vegetation collections. A total of 10,421 data points were collected across 14 days, including 5390 records (52% of the total) uploaded to iNaturalist, comprising 640 plant and animal species. Public awareness of the CS expedition reached over 700,000 people based on estimates from advertising, media, social media, family and friends, and conference presentations. We estimated the total carbon footprint for the expedition as 268.7 tonnes of CO2 or 4.47 tonnes of CO2 per person, equivalent to AUD 112 needed to offset this input. Based on these results, our recommendations to leverage CS methods include governmental review strategies, temporal replication to allow for the measurement of changes through time, integrating sustainability into CS ecotourism platforms, and encouraging broad participation.