The paper illustrates and discusses the impact of an environmental crisis the appearance of an algal blooms in the Adriatic sea during the summer of 1989 on tourist attitudes and behaviours. The tourism basin involved Italy's Emilia-Romagna Riviera is one of the world's most important. The environmental crisis provided an opportunity for evaluating the sensitivity of tourists to environmental issues and for identifying this tourism system's demand segments and the relevant marketing implications. The findings of a survey conducted in August 1989 on a sample of 823 vacationers along the Emilia-Romagna Riviera are reported. The vacationers were asked to indicate the importance of various seaside holiday activities. The ensuing results were factor analyzed and generated Expectability and Sensualism as the two major factors. A cluster analysis was subsequently performed on the basis of the individuals' factor scores and produced five demand segments with respect to seaside holiday-lifestyle. On the basis of vacationers' holiday lifestyles and relevant socio-demographic traits, the paper examines why they decided to visit the Riviera despite the environmental crisis, what changes in daily leisure activities ensued from the presence of algae, how they judged their holiday and the algae emergency, and what kind of impact the algae had on their vacation. It is shown that reaction to the environmental crisis differs remarkably according to seaside holiday-lifestyle and selected socio-demographic traits. The tourist target groups most immune to the algae phenomenon comprised the extreme age groups: younger tourists privilege the infrastructural, urban aspects of the tourism context, whereas the older value factors related to the creation of social bonds and a reassuring, predictable atmosphere. Vice versa, the tourists which expressd greatest sensitivity to the algae phenomenon were foreigners, members of central age groups and people with relatively high social status. The marketing and research implications of the findings are discussed.