Globally, the cruise sector has had quick growth and high revenues in the last twenty years. However, this issue affected tourist destinations and natural resources, causing a steady deterioration. Particularly, there is a growing opinion that the sustainability of this mass tourism is a problem that needs to be addressed and resolved through accountability tools. For this reason, the implementation of sustainable tourism practices has stimulated cruise lines to develop sustainability reports, according to some international tools and in most cases, these companies adopt the GRI Standards. This study aimed to highlight the evolution and awareness of the impacts in the cruise sector by analyzing the sustainability reports drawn up according to the consolidated GRI standards. In particular, in this chapter, some values of the GRI standards, belonging to the 300 series, named “Top-specific Standard - in environment”, have been analyzed and compared. The purpose is firstly to analyze the environmental impacts of the cruise industry, starting from the identification and evaluation phases. Secondly, it highlighted how much a tool, such as the GRI can allow for comparative analysis. Furthermore, this chapter presents a comparison between three cruise companies, on the basis of some values associated with the GRI environmental indicators. Finally, for a specific company, the sustainability reports were compared over the years, to evaluate the company’s approach to the environmental, economic and social performance through the GRI standards. Particularly, the authors identified two hypotheses to be verified: hypothesis 1. The GRI implementation allows an improvement of the environmental performance; hypothesis 2. The cruise ship is equivalent to a city with identified requirements in terms of environmental impacts.